Phil, you dont need 2.5 bar of boost to see 500bhp on a cossie engine, you could see it at under 2 bar easily if it was at 9000rpm
Loads of ways of skinning that cat, not just the way you happen to have tried and failed to do it.
Gareth, I agree, if you strap a big enough blower on (with a massive hotside housing thats laggy as hell and doesnt spool up early enough to have problems with surge) 500bhp on totally standard engine has got to be a breeze, it just wouldnt drive very nicely!