RT660 in 225/40R18, prev had a 245 set but I didn't take care of them. luckily they don't suffer as much with less camber as other 200TWs.
there are actually 2 other people also running a 6 in this region; one's another '14 on Indy500s and the other is a turbo in STS with A052s (I want a turbo 6 seeing how quick that car is). the Firestone is a "bad" tire and afaik the turbo car has coilovers so they can adjust more camber for the A052.
Excellent choice of tire. I wish more people would get into autocross. People think you have to get a highly-prepared race car but all you need is a car and then maybe some good tires.
Do you notice a change in acceleration (using your butt dyno) due to the smaller wheels? I did this once on another car for the same reasons (gearing, lower weight, and in my case, to use the same tire on all four corners for rotating my racing tires) and was impressed with the results at the time. It also lowers the car ever so slightly. All of those things are great for autocross.
I don't personally feel longitudinal acceleration as any different but the data I've collected suggests I'm over 1 second faster to 20mph so I guess? lol