I also don't know about the snow yet, but I just put Toyo Proxies 4 on my 02 GT and they have been great so far. It's been raining all week here in MI, and I haven't had any driveability problems.
SE Michigan area here (St. Clair Shores)
Just picked up my first Mustang 2 days ago, 02 GT Vert. Traded in my 03 Explorer LTD for this. Having fun with the GT so far! It's stock for now, and will probably stay that way for a while.