Ok here is a run down of the 70-200's
2.8 IS - !!!!$1700!!!!! 3.5 lb
pros - 2.8 for super low depth of field, useful when you cant get that close and still want to isolate the subject. Dust and moisture sealed
cons- over priced, very very heavy. large volume
best in low light,
good in sharpness.
decent auto focus speed
2.8 - $1300, 2.8 lb
pros - 2.8 for depth of field
cons - no IS, shakier photos in low light or sports. still heavy. large volume not dust/ moisture sealed
good in low light
good in sharpness
same auto focus as 2.8 IS
4 IS - $1200 1.7 lbs
pros - supper sharp, really good IS, light weight, small volume. dust/moisture sealed
cons - f4 so a loss in depth of field.
good in low light
best in sharpness
fast focus speed
4 - $650 1.6 lbs
pros - cheap, yet still high quality. light weight, low volume.
cons - f4 and no IS, not dust or moisture sealed
meh in low light
good sharpness
ok focusing, it can have some trouble some times.
Overall if I was mainly shooting in the studio I would go with the 2.8 IS, if I had some dough for it. If I was going to ever have to travel with the thing or carry it for more then half and hour I would go with the 4 IS.
Going with an IS is key for me, especially if your using it at 200 on a 1.6 crop. makes it way easier to track a moving subject. or hold in tight on a subject. Since you will be using it outdoors in snow, having it sealed against the elements is a really good idea.
As for the 4 vs 2.8 thing, the big thing for me is size and weight. When you have a pack on your back for the whole day full of camera equipment it is nice to save some weight every where you can. The smaller size is nice since it will make it easier to pack your bag. Also if you ever travel with it saving weight can save you some money on oversized baggage fees. (which add up quick with ski and photo gear).
Its also nice that the 4IS is a bit sharper then the 2.8's. They are both plenty sharp, but its worth noting that the 4 is sharper at every f/stop they share.
I really have no problem going 4 over 2.8 these days. The lens is long enough that depth of field should not be an issue, especially on a 1.6 crop.
With modern ISO abilities shooting f4 and 1600 or 3200 is going to still provide very crisp shots. I guess I see no real handicap for the f4 in low light these days.