Forged is overkill IMO for a winter wheel. Lighter wheels matter to performance but in winter it isn't relevant unless you are tracking your car in the snow
A flow formed wheel is just a cast wheel but of higher quality. It is more than enough IMO. I will use any wheel (gravity cast, flow formed, etc) for the winter. In the summer, when performance and feel matter, I want a light wheel and that normally means forged. Winter wheels should be inexpensive wheels as the conditions beat them up regardless. Cast wheels are strong enough for winter use (although some will argue otherwise)... keep in mind that the vast majority of OEM wheels are cast and very few are forged. All of those cast wheels do just fine in winter. Find a quality cast wheel that you like and just save the money... VMR, Avant Garde, etc, etc...