You might want to peek at our FAQs - What film to use I have taken nice shots with Konica Centuria 200, it usually gave me enough speed to work even with slow AF zooms. Have a great time JRP My profile Previous photography stuff, before Nikonians: A Brief Love Story
I use Kodak Max Zoom 800 on an N80 with Sigma's 50-500, exclusively for wildlife in YNP. Prefer prints due to the latitude they provide. You will need to compensate for the snow, do not let the camera due the work. A priority is the setting I use. Have a great trip, its a magical place, especially the Lamar Valley(hint, hint).
Since you mention Feb. and snow, another concern to be aware of is the temperature. Your camera batteries could "fail" once they've become cold enough. Carry at least one "spare set" some place "warm" (in your shirt pocket inside your parka, etc.).