Eligible cars for the race group, finalized, with PI and designated bucket (legend found at the bottom):

Super GT:

Aston Martin DBR9 (either): 825
Audi ABT TT-R: 827
Audi A4 Touring Car (any): 833
BMW M3 GT2 (either): 809
Chevrolet Corvette Racing ZR1: 816
Chevrolet Corvette Racing C5.R: 817
Chevrolet Corvette Racing C6.R: 823
Dodge Viper GTS-R V8: 823
Dodge Viper GTS-R V10: 823
Ferrari FXX: 837
Ferrari F40C:  852*
Ferrari F50 GT: 875'
Ford GT Mk7: 819
Honda GT500 NSX: 859^
Hyundai FM Genesis Coupe: 859^
Jaguar RSR XKR GT: 814
Koenigsegg CCGT: 857*
Lexus GT500 SC430 (any): 857^
Maserati JMB Racing MC12: 824
McLaren F1 GTR (either): 848*
Mercedes-Benz C-Class Touring Car: 834
Mosler MT900S: 819
Nissan GT500 Skyline: 858^
Nissan GT500 GT-R (any): 859^
Nissan R390 GT1: 859*
Opel Astra V8: 829
Pagani Zonda GR: 825
Pagani Zonda R: 872'
Panoz Esperante GTLM: 810
Porsche 911 GT1-98: 857*
Saleen S7R: 836
Toyota GT500 Supra: 855^
Viper SRT GTS-R: 820

GT:
Audi R8 LMS: 759^
BMW M3 GT2 (either): 756^
BMW M3 GTR (either): 735
BMW Z4 GT3: 740
Chevrolet Corvette Racing ZR1: 754^
Chevrolet Monte Carlo Stock Car:  779'
Dodge Viper Competition Coupe (any): 732
Ferrari F430GT (any): 763^
Ferrari F458GT: 763^
Ferrari 599XX: 787'
Ford FG Falcon: 734
Ford Fusion Stock Car:  779'
Ford GT Mk7: 761^
Holden Commodore VE: 734
Jaguar RSR XKR GT: 752^
Lamborghini Gallardo LP560-4 GT2: 759^
McLaren MP4-12C GT3:  759^
Mercedes-Benz AMG SLS GT3: 738
Nissan GT300 Z: 736
Panoz Abruzzi GT2: 759^
Panoz Esperante GTLM: 752^
Porsche 911 GT3 Cup ('03): 733
Porsche 911 GT3 Cup ('11): 733
Porsche 911 GT3-RSR ('05): 760^
Porsche 911 GT3-RSR ('07): 756^
Porsche 911 GT3-RSR ('11): 760^
Subaru Impreza GT300: 737
Viper SRT GTS-R: 751^

Legend:
^ -5% handling (GT500 GT2 GT4 bucket)
* -15% power (GTS bucket)
'  -25% power (Supercars bucket)

Edits: reduced PI from 735 to 725 for modified street cars in GT. They were just too fast for the handicapped race cars. I included some cars that I just looked over and then modified some of the cars' PI to get them more in line with the others.

Street cars are gone from GT. They just didn't fit with the speed/handling balance that I wanted. Look for them in the SS class in the upcoming season(s). As a sort of balancing post-script, some of the race cars eligible for competition in either class have to stretch a bit to be competitive, and some are even at the end of their rope as it stands. So, if you don't think that you'll be very competitive in a car that already has been maxed out, I might advise picking another car, as mid-series balancing will be handled via adjusting tire width.

im calling shinanigans. my porsche GT1 is WAY to slow in a 15%.... not even kidding 440~hp after the 15%... and in practice i get DUSTED in every straight..

--but you have crazy handling.

Compared the that Mosler...? Nah he beats me int eh corner and then leaves me in the straight.