Ahoi!
In your position I would buy an olive green Snugpak Special Forces Complete System, eventually with olive green Snugpak Special Forces bivvy bag (if you don't already own a Carinthia Goretex Sleeping Bag Cover), a Ullfrotte Woolpower 200 turtle neck shirt and under wear trousers, a Carinthia LIG jacket, Carinthia LIG trousers and Carinthia booties.
That will surely serve you very well in Canada, Sweden, Norway, Finland and Poland, even European parts of Russia if you see all that as your sleeping set up. (The clothing may not be warm enough in the evening though.)
But if you come home you can disassemble it to a lightweight summer /3 seasons sleeping bag with ultra light bivvy bag for temperatures until 5°C or if you are tough until 0°C and a sleeping bag for usual Czech winter weather, altogether it is rated for -20°C what's the lower end of temperature that you have to expect in Czechia in pretty rare cases. And the LIG suit alone you can wear in normal Czech winter weather if the Ullfrotte Woolpower underwear isn't warm enough. Or you can change one with the other on longer winter tours in central Europe.
The Compression bags of the Snugpak Special Forces System you can gift to your Grandma as pillow cases an buy yourself instead of that the superior Carinthia military compression bag in Large size with 4 vertical and 3 horizontal compression straps, that you can use either for only the Snugpak Special Forces 2 with bivvy bag or the complete system including either the Snugpak SF or any Goretex bivvy bag.
All the equipment that's mentioned above is tested and used by Special Forces of several NATO armies, similar to the Carinthia military sleeping bags that are in my opinion in your special case only the second choice.
The modular sleeping system by Carinthia consists of the Tropen that goes into the Defence 4 and both into the Goretex Sleeping bag cover. It's faster assembled than the Snugpak Special Forces System, because using the Carinthia system you just put the summer bag into the winter bag that's already in the bivvy bag, but these sleeping bags have different to the Defence 6 and the Snugpak Special Forces 2 no warmth collar, what is rather unpleasant at -20°C although it works, especially if you wear a padded suit like the LIG in it.
The SF2 goes into the SF1. Or better: If the SF2 isn't warm enough you have to pull it out of the bivvy bag and put the SF 1 around of it, zipp it together with the seperate adapter that I always keep in the zippers of the SF2 and than you put it all back into the bivvy bag.
You surely understand why most European NATO armies decided to issue the Carinthia system.
But well, the SF system was delivered to the US, Australian, British and Latvian army. In older times they issued to officers different kit than to usual soldiers. The officers kit was a bit finer and nicer. The SF system is compared to the nearly identical modular Carinthia system such a nicer and finer "officers kit".
Its far more comfortable to use if you aren't in a horrible hurry. You have here the comfortable warmth collar in the inner winter bag and after assembling all you have just one central zipper to enter or leave both sleeping bags, just the bivvy bag has its seperate zipper.
In the modular Carinthia system you have 3 zippers to open and close! Yes, they surely all leave the zipper of the Tropen open if they use the complete system unless the system really reaches its limit.
The SF1 and the SF bivvy bag fit well together in a 7 litres Ortlieb dry bag PS 10, available in black but perhaps you still can find a olive green one, just stuffed by hand, if you want to use it in your area in the warmer month.
The Snugpak Special Forces Complete System fits well into the Snugpak Drysack 35 litres, available in olive green too. Doesn't matter if you use the Carinthia or large Snugpak compression bag.
Carinthia equipment is developed in Austria and made in Moldavia or Czechia using the own Austrian filling.
The Snugpak Special Forces sleeping bags are made in Britain using a Swiss filling. The SF bivvy bag is made in Vietnam but very good.
You can see all that stuff in Salzgitter in the shop Recon Company if you want.
The next youth hostel is the modern and well located house in Braunschweig.
You walk from the railway station Salzgitter Bad approximately half an hour to Recon Company which is located a bit outside. It's worth to take a head torch with you, by the way, should you come back late.
To go there would especially be sensible if you also plan to buy a large rucksack to carry all your winter equipment, because the lightest 110 litres military rucksack is made in China by Berghaus, its the Cyclops 2 Atlas 4 that was improved by the Special Forces before it was issued to the German army. It's the cheapest of the serious large military rucksacks too but it's sensible to try it on in the shop because they sell it in 4 different body sizes like clothing! If you are interested in also this you should try it on and not just order it in the internet.
One could of course as well decide to go the national route and buy a Czech made in Austria developed Essl rucksack. Or a in Germany developed and in the Czech republic produced Fährmann rucksack.
Or whatever, the Berghaus Atlas has a lot of very similar competition. I went for the lightest and cheapest of the serious ones.
A Rucksack that's developed by several NATO armies over decades and used by German Special Forces should be OK for my rather smooth use I guess.
I mainly bought it because my complete equipment fits perfectly in there. The compartments simply have the correct sizes for current military equipment.
The German army recently decided to swap to Snigel and Tasmanian Tiger by the way and ordered 30.000 of each.
But I think that's all more or less the same.
Back to your original question:
Ray Mears' offers seem to me to be generally over priced. On top of it you would have to pay serious import taxes.
Apart from Mr Mears himself nobody is convinced about his sleeping bag quality and you surely will find nobody who tried his winter sleeping bag, because the Canadians use American products, Snugpak and Carinthia and we here use Snugpak or Carinthia or copies of Carinthia products. But especially the Brits rarely own so extreme warm winter sleeping bags. And only Brits seriously consider buying Mear's overpriced stuff, because he is popular there and nowhere else.
Infomed bushcrafters of other nations usually just buy what's issued in the army and it's fine or get high quality equipment from civil brands if they don't run around with outdated traditional stuff from grandpa's times. Most British bushcrafters do that too of course.
May be that I am wrong and you will get a serious review about the Ray Mears winter bag here, but I doubt it.
The Carinthia Defence 6 is a good sleeping bag of course. If you have enough money to buy a sleeping bag that you can use in Czechia only in January and February because it's otherwise too warm, so go for it and combine it with a padded Carinthia suit like the LIG and Carinthia booties. It would save you weight of course compared to the modular sleeping systems that I explained above.
But that's rather a sleeping bag for the Alps or perhaps Zakopane during the winter.
I wouldn't buy it just for a short trip to Canada or Scandinavia. I would probably buy it if I would live in Austria, south Bavaria or Switzerland though.
Something different is if you are unusual small or tall. Than you should look for the sizes of the bags that I mentioned here. Carinthia offers also sleeping bags for short guys, Snugpak also for giants.
But at -20°C or less you stuff your clothing into the foot box of your sleeping bag, and perhaps also electronics and water bottles. Don't choose the sleeping bag as short as your tight fitting summer bag!
I generally don't recommend red sleeping bags to people who could consider using it in central Europe. The legal frame here is so tight but otherwise forgiving that a well chosen stealth camping equipment is the way to go here! Such large things like tents, tarps, sleeping bags, bivvy bags and rucksacks simply need to be oliv green or decorated with a camouflage pattern that blends well into the area.
But plain olive green is invisible in Czechia, Saxony, Poland, Austria and Bavaria too of course. It's invisible nearly everywhere in Europe.
You can walk from Prag straight to Bordeaux if you don't disturb anybody and sleep where you want. But you are tolerated and often don't have the right to sleep there in the open landscape.
And I am pretty sure that foresters, farmers and hunters who wear olive green themselves prefere those who use it too.
