The most important thing is for it to withstand the pressure caused by ice and snow on your paint and offer itself as a renewable scarificial barrier rather than your paint.
The 476S is a lil more difficult to apply than the 845IW, but offers an additional 1-2 months more protection than the 845IW. The 845IW is good for about 4-5 months of winter carnage and the 476S 5-6 months. Applying it is very easy if you follow the instructions I provide you with. I suggest you try the 845IW for all around praticality.
This stuff is legendary in the boating and aircraft world, its just catching on with car detailing heads in the last 5 years. At least a dozen MR members have been using it for several years.
I use Collonite wax since 2 years ( the two of them) and all i can say is this wax is the best i ever try and i tried alot. I never bought something else after that. Very good wax.