With MPH like that (considering you had no traction) and slicks, I really don't see why you can't run 12's? Shaving .1 of your 60' is worth .2 at the end of the track. Your MPH will be even higher if you're gripping rather than slipping, and 1.9 60' times are possible if your suspension is up to it.

I fit Nitto 555R 225/50R16's on a 6" rim. 4 of them. As long as you're not auto-xing they should work great. I ran 16lbs in the fronts and 26 lbs in the rears. The whole contact patch hit the ground. EDIT: But my car is 3355lbs with an empty gas tank.

Just my 2¢.

PS: ahhh... those Buick Regal GS's (Grandpa Sport) are fun aren't they? I did some investigative work in one of those... Nobody notices them, nor can they get away if they ever do. Just add a baby seat for extra sleep-factor. Flippin' things are fast, man. & a heckuv a lot of fun, too!