The GT35R is already more than enough for either engine, provided you have the right turbine housing, which you allude to not having but don't specify which one you have.
In point of fact, for road racing, I would consider the 3076 w/a .82 exhaust housing (~same flow as the .63 GT35R housing).
Area under the curve is far more critical for road racing and I think the lower end response would really help more than later top end power...
You haven't mentioned how much boost you want to run either, so until we know more specifics you're just gonna get pot shots/guessing at what would be appropriate.
Not sure what you mean by later technology, the 6262 that you refer to seems to be a Precision turbo, and there is no "later technology" there.