Basically there are two turbo's which are refered too as T38's, and both seem to work very well.

One is what I have which is Universal Turbo's Version, and the other is Turbo Techniques Version, which is infact slightly larger. Both have different driving charachteristics, and it really depends what you want from your car.

Big Punch, Minimal Turbo Lag, and Reasonable Power..... Go for Universal Turbo's version.

Big Punch, slightly more lag, and the possibility of slightly more top end power, then people tend to like the Turbo Techniques Version. Both Very Very Good Though.

Remember though, it's not all about big bhp numbers, it's how the car drives. No good having 500 bhp at 7000rpm, and no power below 6000rpm. Better off with say 400bhp between 3500rpm and 7000rpm in a nice long power band.

Obviously alot depends on the rest of the engine, but your spec sounds similar to mine, so should give you a good indication of what is possible but only with all the right ancillaries.