I have an 05GT w/ 18in wheels & Pirelli all-season tires. I drive it through the winter as it's my only car. All I do is throw a couple 50lb bags in the trunk. Sure its not going to handle like a FWD or AWD car, but it can be done without too much effort. There is no way I would pay for another car/insurance/maintenance for a few bad days out of the year. And nothing is rusting out either!
I will say if you get the 19's some cheap steal rims and snow tires may be a good idea. Thinking about doing that myself w/ the 2011.
Currently: 2011 Mustang GT - Red Candy Metallic, 6AT, Premium Pkg
MODS: C&L CAI, custom dyno tune, Boss IM, UMI stb, J&M LCA's, Boss front facia, SHR louvers, GT500 rear diffuser, GT500 splash guards, JBA headers, catted x-pipe, Roush axlebacks, soundtube delete 386 rwhp / 368 rwtq (4th gear), 1/4mi 12.52 @ 115.3 w/ 2.00 60'
Sold: 2011 V6 MT - 1/4mi 14.28 @ 101.1 w/ 2.3 60'
Sold: 2005 GT 5AT. Steeda CAI, BBK headers, Bassani o/r x, JBA axlebacks, 280 rwhp / 300 rwtq, 1/4 mi 13.43 w/ 2.1 60'