Garrett has a whole line of GT-series ball bearing turbos. The GT28RS just happens to be a step between the GT28R and GT30R, and that's why they stuck the S on the end.

Brtecson - a Honda VTEC motor (properly built of course) would probably be able to make more power with the same turbo than an SR20. It can rev higher and generally speaking the heads flow better.

Theoretically speaking with an ITR motor to put 400 hp to the wheels would require about 20 psi of boost. That's past what the GT28RS will do on an ITR motor. A GT30R should be able to flow those kind of numbers no problem though.

All of this is assuming of course, that the motor is being built to take this kind of abuse and you have the means of dialing it all in.