Why would you buy their pass and only ride their trail system? Must be an old boys club mentality running that club? I support the ASA. I also prefer to ride many trail systems.
Its probably an 860. Don't think you can go much bigger in the bore, or else someone (aftermarket mod shop) would have done it already and it would be more popular.
You can use the local weather cameras for conditions and see for yourself. Doesn't look good right now. I used to go in february on the long weekend and always lots of snow, last few years its been hit and miss. Strange for an area at 6666' elevation in town.
West Yellowstone, MT Weather...