Having had 2 SR20DET powered Silvias I can tell you the RB is more then a match is pretty much all aspects, they all had the usual filter, boost, exhaust, nothing serious.
The RB sounds much nicer and you don't feel like your killing it at 6000rpm like the SR.
The RB25 is obviously gonna make more power as its a bigger motor but the car weighs more so its not really a comparison anyway. If you wanna compare, then compare the RB20 and the sr20
I would choose the RB20 over the SR personally....
Most people put RB25/26s in R32s rather then do up the RB20 when it comes to drags.