tire width, wheel size and performance

These topics have been discussed in times past but there are new tires on the market. I would like to direct this thread to 07 spec b owners (or later if the suspensions are the same. I am an aggressive (or spirited ? driver) who runs occassional autocross. I have stock suspension at this time. I am getting new 18" wheels and want the widest tire I can put on either a 7.5 or 8" rim for the best overall performance. I thought about geting a dedicated autocross tire but for right now looking for daily driver tire with good or great handling and cornering in wet and dry. My thoughts in looking at tire rack suggest Michelin Pilot PS2. Is there really a significant/noticeable difference in handling between 225, 235 or 245 tires for this kind of driving. I don't want to roll the fenders or make any other modifications to get the tire/wheel combo to fit. But I also don't want to get something I don't need. I am a novice autocrosser who wants to improve. In short, what size tires and wheels are you using, and what offset are you spec b'rs using for max all around summer performance on our stock cars?