Mine is stock, and I have to say I'm impressed with how well it handles in the snow. We've had 2 pretty significant snowfalls this year, and the only place I've had trouble is getting into and out of my neighborhood it's pretty hilly.
The first day, coming home from work semis and other vehicles were getting stuck, but I didn't have any trouble, even when I came to a full stop on the uphill side of a bridge. I was stunned
Then I got into the neighborhood, and we have a new family who didn't realize that parking their car on the side of a curved road going up a hill isn't a great idea. Since I was more worried about hitting their car than getting up the hill, I left it in the pool parking lot and walked home - safer for everybody. After I was able to get my stang home, the next day my husband and I were leaving for work, and I made it up the hill, but his Mini Cooper wasn't so lucky - he was happy to get back into the garage.
My goofy neighbor across the street was telling me that her husband'3 300M has "that rear wheel drive, and he can't make it up the hill". Her eyes bugged when I mentioned that mustangs are also rear wheel drive - I think the lower horsepower of the V6 really helped me out, which is good, this is my daily driver and all...