I switched to Pilot Super Sport last spring and they are GREAT!!!
They have more dry grip, and way more wet grip, than the stock tires. Way more. Traction control light even comes on less often (Dinan stage 2 software). Ride is WAY more comfortable with non-run-flat too. End the treadware rating is higher.
Consumer reports (I know, not car enthusiasts, but still...) rated super sports 10% higher than the #2 tire(s).
As for rear size, it won't matter much, it is only 1/3 of an inch. Might get a little less understeer. Gary @ Tirerack once told me that many autocrossers run square setups (225 all around) so the car "rotates" around sharp corners better.