I sort of understand what calum is saying. But personally, I'd run it by the numbers. I have no experience with rolling roads, Dynos and rebuilding engines etc... But I have plenty of experience with getting the maximum of performance out of computers. Now you can build yourself a nice rig and all and it can run your programs, engines, games or whatever absolutely fine. But if you don't tune your rig and set it up properly, then you're just losing some of the extra kick. And in which case, I then have to go and run the numbers
If you're happy enough with a smooth ride, that's fine. If you want to push it to the limit then you'll need the numbers.