40K-50K is a competitive market now. The days of picking up a cheap WRX to blow away M3s are over. Them handling on the last cars was weak-sauce out of the box.
I think you're underrating the STI's handling. sure it's no M3, but it handles extremely well... as a road car. I was kicking myself for not getting out to a track day, but it just didn't work out. but still, from what I felt on the road, it seems like you can manage all that power effectively on a track, and light modding - like Mike's big anti-roll bar in the back - should turn the handling balance into something very capable for the track.
aside from the Evo, which has a slight edge (with a trade-off of even more intolerable cabin noise and harder ride), what car is faster (track or not), cheaper and better suited to a snowy Canadian winter?
Personally, I'd sign up for Golf R (interior, refinement, feel, transmission), but that understeers even more obviously, even at public-road speeds...