You gotta drive the SRT10 with the throttle; whereas the ACR is more of a race car, and you can use more steering input and finesse. Honestly though, in laptimes it should be no competition, the ACR should absolutely murder it. I just like the SRT10's insane torque with low downforce - you can spin up in 4th on the Nordschliefe on sport soft tires at over 120mph, which for some reason, puts a smile on my face. I do have the suspension tweaked just a little (just my basic crap I do to every car, really, no tuning), so maybe that is making the difference.
The ACR is just so much more planted, and I think it drives very well with 1000hp; much better than I thought it would anyway. It seems really weird to me that you are 2 seconds slower with the ACR than the SRT10 @ Laguna? Handling is the key factor, not torque, and the ACR does indeed corner miles better than the SRT10.
Maybe I have another weekend GT5 project/shootout : )