Guys, this has been a fantastic discussion. Much appreciated on all sides, and really cool to me that guys who make the rules get on here and discuss how they are made.
I'll kick in my two cents -- after reading all this, I agree with Scott and others. Let's deduct weight from the existing S cars and keep the Bimmer at 325. I think most of the front runners can do it (I'm an oddball, TR8, but at 2560 I run 50 lbs of ballast and a full tank of gas at 185 lb driver to make weight, so I can lose weight). I think the GSR, the 944, the 240z, definitely the 260z, the 280z, and the RX7 can all drop a few as well.
Darin, I liked your spreadsheet on ITR. It is a "different" enough group of cars that I think S remains viable. Also, the price of entry is high enough that I think it will be more like T1 and T2.
In any event, good discussion.