yeah, RB25DET is not so expensive =D
my normal plan was 2 put ~450 - 600bhp on the engine, on RB20 is possible but i've 2 do a lot of work on it 'coz the stock internals r good for ~450bhp, i've read about the RB30DET and was impressed of the power, ~420bhp and 620Nm, that is great! there i would put a Garrett GT30/40R on it and it is fast as hell =D
oh yes, i want 2 use the RB25DET tranny but anyway, i think the RB20 will also hold that power, a friend told me about 240ZX with RB20DET tranny and ~600hp and it still holds that power =D