Poco

I've run 3500 miles so far on a lowered staggered set-up,18x9's 255-45-15's/18x10's 295-45-18's.I taken a couple of 400 mile trips,drive up on mountain twisties and lots of metro freeway driving.I had some bounce issues until I replaced the stock dampners to Steedas Pro Action non- adjustables.It did firm up the ride and took that bounce out.
Honestly I did it for an old school look but if your driving your Mustang daily just run a matched set of wheels and tires.You will have the best of all worlds.You could still thrash it,drag race it or run some twisties and the car will look good and handle consistantly.

Silos_and_Sirens

I think I am sold...Keep the 255/45 18's in the rear, and leave the stock 235 50 in front. I chose the BFG KDW for the rear-rated at 99Y, insted of the 97W. This was perhaps my best mod, the car feels sturdier, handles better, stops, goes, and even is more comfortalble. This also lowered the rear slightly, along with the steeds kit I recently installed. It also looks sick. I will post some pics very soon.