Ah ok... so all R33's have ball bearing, series 1 is ceramic intake wheel, series 2 has nylon, R34GTT has bigger housing, ball bearing, and nylon intake wheel.
Pretty sure that's right!
As for how much boost you'll get, you'll get whatever your boost controller is set to! Stock boost those turbo's see is 7psi, but many people run them at 10 or 12 psi safely. Obviously the R34GTT with the bigger housing could take a bit more, but remember that your RB20 motor is not pushing as much exhaust gas as an RB25 motor does, so it will take a little longer to spool these turbos, so don't go too big on a stockish setup.