Thank you for the great info, Minihune!

I'm pretty sure that any of those combonations will result in at least "mediocre steering resolution" or better, which is cool for me. For 17s, I'm leaning towards the 215s for a wider, more rim-filling tire.

As far as 18s go, I have 2 concerns:
-Ride quality. I think the ride difference b/w 17s and 18s is small, but still a factor. Colorado has nice roads, but there are still sections that are dangerous for wheels, which leads me into my second concern-
-Bent rims. 17s will probably never get bent, even on 215/40s, but 18s on 215/35s are much more vunerable. I don't want to have to shell out $200 or more every time I (or my girlfriend ) catches a pothole.

More people with 18s are saying the "negative vs. positive" isn't as lopsided as I first thought. After all, it's just an inch.