Softie 3's are summer weight bags, they have virtually no loft. I have been using a softie10 for at least 10 years, year round and in some pretty awfull conditions, this is supposed to be a 3+ season bag, I have had no problems with it.
I also have a sleeping bag made by Mountain Equipment, which is also 3+ season, this is marginally warmer, but the construction is not as robust and this has been overlocked.
I have a down bag which is rated as a spring summer bag, this I have used all year round as well, this on the other hand got a little nippy in January on the side of Pen-Y-Fan with a gale blowing and the snow coming down, but seeing that it is not rated down to that level it was not expected to be brilliant. Using the layer system as a guide I got the bag to a temperature that I could sleep quite happily.
In conclusion all sleeping bags are different, despite what they claim on the tin they do not work for everyone down to the temperatures that they say.
My 2 season down bag has better loft, compresses smaller and pound for pound is a far better bag than either of the other two, its rating should be 3 season and with a bivvi bag could possibly get away with 3+.
I may well be getting a Wiggy's bag soon that is rated at the same level as my down bag, I would be highly surprised if it could match the size, weight and comfort factor of the little down bag.
