Best to talk to your engine builder and mapper.
All depends on how safe you want it to be.
With full control over boost, ignition, fuel and cams you will have many options.
I run a HKS tt Roadster with 525hp at the huds (around 600 at the fly)
I am amazed that you did not figure/calculate all this out prior to starting on your project.
I also would have thought that torque would also have been a major issue.
Remember bhp sells cars, torque wins races.
Do your searches on both U.K. forums and educate yourself
After that, feel free to give me a shout anytime and I will answer all your questions with informed responces.
As a matter of interest, who is your preferred engine builder and mapper?
Cheers,
Alex.