8K is a walk in the park for a stock RB20. I simply raised the rev limit on mine (Nistune) to 8300 and ran it hard for years. Stock turbo though.
9k is not hard. Just need springs, and maybe consider the lifters as a potential weak point. Making strong power up there is, of course, a matter of cams and porting and so on, as I said before.
Doing all of this, on a forged motor, and not planning to run 22+psi is a waste of time. You need boost and you need lots of it to make power on an RB20. With E85 you should probably be considering 30+ psi.
An RB20 is not a good motor for the street. By the time you have them up into the 250rwkW region, you have lag, lag, lag, lag, nothing, then more nothing, then.......wheelspin. As a track engine, kept right up on the boil, more acceptable.
For street use, I would seriously not be looking too exceed 200rwkW on a 20, to try to keep it more useful. But even that still matches the description in the paragraph above. I went RB25 and the thing actually accelerates before boost arrives, simply from that tiny bit of extra capacity. A 3L would be even better.
If I was stuck with an RB20, I would twin charge it. Screw compressor blowing through a turbo. Make it act like a 3L, then rev like a 2L. I think I might have said this before.