handling car 17's or 15's?

Good points Keating. nice rims/tires aren't all you'll need to take the turns fast.
Abodyjoe's dart is riding on RMS suspension front and rear, so its kinda hard to compare ride caracteristics, but I'm betting it drives real nice.

I've installed a B body rear on my car and i get a little over 1" clearance either side on the rears, without spacers, using 17x8 Cobra rims with 245/45 tires and 5.72" backspace. with the extra room provided by using B body rear, i'm seriously thinking about 18x9 FR500 rims using later mustang backspacing, but i need to triple check fitment on the front before pulling the trigger.