Dale,
A bloke who runs on the same dyno as I has a GT28 on his RB25, comparing the dyno graph to a stock turbo'd rb25 the spool/power is almost identical down low and then the gt28 simply takes off and makes an effortless 240rwkw, I don't remember what boost it was running but it was fairly low, I remember thinking wow wind the boost in to it and that would really have some killer mid range (not that it already doesn't).
It really did look like an awesome street setup.