550 is very good. I think Barry's car (Steve's old car in California) made 549 at the wheels. Best number I remember seeing.Well I think my car achieved pretty good results with just 8 psi and stock headers compared to another similar setups. I'm sure 550+ is not a big deal with headers, new pulleys and a retune and I'm planning to proove it. Since one healthy M5 is capable of 600 wheel I don't see a reason why I couldn't?
Make sure you get to look at the AFR's. You need lots of fuel, in part to help cool the intake charge. Compressed air generates lots of heat.