GT28R is the big ball bearing turbo.
Several folks are getting 300-325 out of these in 2 liter applications.
I am running wussy levels of boost (12) and still getting 260 on a built 1.8 with full boost at 3100rpm, so they spool real fast, no noticeable lag.
Could be run at lower boost levels (7-9)in a 3 and still get 300ish without much stress.
Obviously the T3/4 will give you much more bang, but I'd worry how much you might be stressing the drive train. Not a lot of parts out there for that yet...