Yes you can use the old cup on the new stove. there is a little gap but did not notice much of the difference taking into account one is stainless and the new one is ali and thinner so will conduct heat better and quicker. you gets what you want. For me even at work if I want some water cooked fast as possible i will use my jetboil so overly concerned with actual boil times. for me this set up is kept in my webbing as a back up or immediate cook set up i carry different fuels and will still go back to hexi if that is all i can get when out on exercise or tour (they do not issue out resealable gas canisters to us
)
As for the old cooker compared witht he new, the new cooker is a lot taller and means that you can put sticks and other fuels into the stove or use some of the new stuff bcb is producing. I have tried it with the fire dragon stuff and the old green snot and it works fine with that, as well as hexi and a lipsil meths stove set up and it has worked fine with them all. I have also tried it with sticks and wooden kitty litter and it worked with that as well. I would say the cooker is a lot better than the old one, being lighter and more efficent but the cup is not althoug deeper i prefer my old 85 metal mug or the crusader mk1 mug but you do need a lid with both. I have several by our very laundich and use them regularly and add so much to the spped of boiling and cooking and have even used one as a mini fry pan
So after of all my testing with this set up, I have my waterbottle pouch loaded in this way.
set up 1:
Crusader MK1 mug on the base
issue water bottle with new GSR adapter
Crusader MK2 cooker placed over the top
down back of the cooker/bottle set up a laundich metal lid
next to the lid my racing spoon
In the lid of the pouch I have a mini clipper lighter and 2 set of puritabs (20 in all)
in the front lip of the puch a flat french hexi stove and 2 pack of dutch hexi tabs ( NSN 9170-12-121-3697 I got several packs when I work with the dutch airmobile recce back in 99 and keep them in my webbing since, yes they still work as well
)(they are thinner and smaller than the Brit ones)
Set up 2:
Mk2 cooker on the bottom
issue Waterbottle on top
metal '85 mug top
and all the rest of the kit of the pouch is still there.
The second set up is slightly lighter but I have not weighed it all as the pouch is on my webbing.