RUF's are open to debate, but my argument would be the more cars to choose from the better really...
I think two classes will be needed, I know the HKS CT230R is pushing 580-600PP whereas some of the others like the Gran Turismo 350Z are languishing at around 480PP.
I can get almost all cars into two classes with unlimited use of ballast and power limiter.
575PP & 490PP
Two cars just don't fit anywhere. Spoon CR-Z with max PP of 459 and Spoon Integra Type R with max pp of 463.
575PP on Sport Soft Tires
AEM S2000
Amuse Carbon R
Amuse NISMO 380RS Super Leggera
Amuse S2000 GT1 '04
Art Morrison Vette
Blitz ER34 D1 Spec '04
Buick Special '62
Callaway C12 '03
Grand Touring Garage 1970 Ford Mustang Trans-Cammer
High End Performance G37
HPA Motorsports Stage II R32
Mine's BNR34 Skyline GT-R V-spec N1 base '00
Nismo 400R '96
Nismo Fairlady Z Z-tune (Z33) '03
Nismo GT-R Road Going Version '95
Nismo Skyline GT-R R-tune (R34) '99
Nismo Skyline GT-R S-tune (R32) '00
RUF BTR '86
RUF CRT "Yellow Bird" '87
RUF CTR2 '96
Tom's X540 Chaser '00
Cars that can fit in 575PP with ballast and power limiting:
Amuse S2000 GT1 Turbo
Blitz Dunlop ER34 Skyline '07
HKS CT230R '08
HKS Genki Hyper Silvia RS2 '04
HPA Motorsports FT565 twin turbo Audi TT
Mine's BNR34 Skyline GT-R N1 base '06
490PP on Sport Hard Tires
Amuse S2000 R1 '04
Amuse S2000 Street Version '04
Gran Turismo 350Z RS
Mine's Lancer Evolution VI '00
Mugen S2000 '00
Nismo 270R '94
Nismo Fairlady Z S-tune (Z33) '02
Opera Performance 350Z '04
Opera Performance S2000 '04
RUF 3400S '00
RUF RGT '00
Spoon Civic Type R (EK) '00
Spoon S2000 '00
TRD Celica TRD Sports M (ZZT231) '00
Trial Celica SS-II (ZZT231) '03
Orphans:
Spoon CR-Z
Spoon Integra Type R (DC2) '99