You don't even need the Orecas. It seems many people here think the ZR1 handles better than the Viper. I find it the opposite, so I wonder if maybe people are biased by fictitious rumor that the Viper can't turn (I know there is a Viper in my avatar, but I don't think I'm being biased lol). Something like
ACR > ZR1 = SRT-10 > Z06. [RM's excluded of course, also, I demand a RM Viper ACR from PD]
is what I expect in GT5. Not sure where to put the GT, I haven't used it as much. It was very good in GT5P, maybe too good.
In reality (going by lap times), the ACR is the fastest followed by ZR1, then Z06 Carbon (not in game) maybe tied with 08 SRT-10 (not in game), then GT, then Z06, then SRT-10.