The thing to remember is don't try and push too much for high numbers. High numbers can be gained very easily but sometimes to the detriment of driveability.
TBH numbers are all bullshit and bragging rights to me. I'm not bothered about what figures my car gets. I raced a guy in a 230 BHP
ibiza in my standard 210 LCR. Now on paper there should have been a bit of difference with a lighter car blah blah blah, but there wasn't. Now if you have a very well set up car that is running a strong 300 ish BHP with good torque figures I think you'll be far happier than if you have a car with 320 BHP and lowish torque that only peaks at say 5,000 RPM then dies.
What I'm saying and other people are trying to say also is there is alot to be said for a well shaped graph, feck figures and feck bragging rights, get on a track and drive a very well set up car with ARB's and coilovers with 300 BHP and 300 ft-lbs torque and tell me after that that your not happy.
Try not to over engineer your set up in your mind before you even get it, have faith in JBS and tell them what you want out of the set up and leave it to them. Don't threaten them with other RR's. If your not going to be be happy with their figures then either don't get any or don't pay attention to them.
Yoiu obviously spending alot of money, if you don't trust them then go else where. If they say they'll get you an honest 310 BHP then leave it at that