Have heard good things about them.
Not looked into the GT series.

bhp is not that big an issue witm me as i am building the engine for good quick strong spool up so high bhp figures are just an added bonus.

It made 477bhp / 422Lbft in it's current guise on Norris Design's dyno last time but i have changed a few bits so just fancy the RB T4 to compliment the changes.