Yep, if you are using a 450hp turbo i would thin that its possible cams may help you out. I personally would not try anything bigger then 256/8.5mm Poncams.
I tried some 260/8.8mm cams and whilst it sounded so cool and tough, i lost power. Bascially killed the engine as it simply didnt have enough compression or cylinder filling and then when the cams would have finally come on at the higher revs all the gases were being choked by the little 8cm housing on my TD06-20G,
So in went the std cams, and got all the response and power back.
Dont forget that RB25s run more compression then the RB20 and they also hae VICS which is why they often get nice results with cams.
I am toying with the idea of again trying some cams in my new motor when/ if my std RB20 blows up. I will be just cleaning up the head (no porting i want to keep velocities high to get good cylinder filling) and bumping static compression up to 9.2:1 and then using 260/10.25mm cams which will effectivly lower dynamic compression of the motor. But to go with this i will also have a few cc more displacement courtesy of 4mm oversized pistons and a bigger turbo with less back pressure at high boost...and also a plenum that many clean up flow a little.
But for a std RB20, i would only try the 256/8.5mm cams with the std springs as i suspect they will be about as big as you want to go.
Just look at the std cams in the RB20, RB25 and RB26 and then consider the displacement and compression of the bigger engines and you will see that the RB20 runs decent sized cams std and unlike the SR20 which really needs some cams in the early to mid 200-250rwkw range...the RB20 seems happy with std camsa