Well, I am not a guru but I can tell you straight up a 2JZGTE can handle 600+hp in factory form. An RB26/30 is a purpose built engine and will handle as much as the parts you can afford to put in it.
One of my mates has a mk.4 2jz supra, came from japan pushing 300rwhp and ran a best ET of 12.7 (with slicks).
Another mate has an RB25/30DETT, made 310rwhp @ 10psi but never saw the strip like that. Now makes 494rwhp @ 21psi.
The RB engine at a similar power output felt a bit harsher than the 2JZ but that was probably just turbo combination and the fact that he was only running a rev limit of 5500rpm at that time as it was leaning out.. full boost by 4000rpm and hit the limiter at 5500rpm! Now, I never drove this car with the RB30, only when it had an RB20.
I did however drive the supra around the time the owner ran a 12.7, it felt a hell of a lot smoother and with the sequential turbos starting to boost ~2000rpm, the power delivery felt very linear.
The supra was pretty much factory and the engine came in that car, the RB on the other hand is in a VH commodore.. so it's kinda hard to tell