I've finished a bit of testing tonight, might get more into it tomorrow, but for now this is how I see it:
Indy Road Course
M3 CSL 03 1:33.585
468HP/8800rpm-1385kg-PP529
M3 Coupe 07 1:34.428
520HP/9100rpm-1408kg-PP534
Z4 M Coupe 08 1:36.024
443HP/8500rpm-1375kg-PP512
All cars w/ Racing Tranny, All drivetrain upgrades, Full Adjust Susupension(not tuned), Racing Hard Tires
The CSL handled the best, wereas the Z4M wasnt too far off, and the E92(v8) handled the worst by a significant margin(but not dramatic). The problem here is the Z4 is maxed on power even if it is the lightest, but still is now were near the other two cars. Even more interesting is the lap in the Z4 I had some perfect corners that I couldnt match time on; so a theoretical best lap for me couldnt be too far off in that car and I feel I had possibly my best lap in it.
Overall each car's top lap are all consistant within I'd say a .5 second, meaning the consistancy of the testing is roughly close to a quarter second give or take from any lap. If the ingame analysis could take top sector times a show a theoretical fastest lap this testing could be have been more accurate, but not significantly different I'm sure. The times arent close at all to consider having the 3 cars be competitive with equal PP. I mean theres like a PP20 difference, thats not gunna bring the Z4M up 2 or 3 seconds. Tuning could change things, but I only see it as making things between the CSL and M3 E92 competitive as they are with these specs, and the Z4M needs more power(by decreasing the power of the 3 series') resulting in a high PP.