If you want to do an RB swap there is nothing wrong with the RB20 or 25. A couple weeks ago there was an RB20det in a s13 with minimal work on it, I think just a BOV and a couple other little things that was running the SAME power as a BMW 850i V12 ( I think thats the right model number). Both cars put down 220 rwhp. Which doesn't sound like a ton but in perspective, a BMW M3 on the same dyno put down 260 rwhp. The guy was running I believe 11 pounds of boost. I run 10 psi on my RB25det and only made 210hp on 10psi, and I have a ton of bolt ons, however I have yet to tune ! The guy's major complaint with the engine was that he has broken 3 trannies in the car, which shows the transmission's weakness, its really just a KA or SR tranny with a RB bellhousing.
Any how I do not believe you should discount the RB20det it can make great power.
My vote on the VG series is that they are strong engines but awful to work on. Maybe its because Im used to working on a straight six I don't know ...
In the end do whatever you want, it will work out well as long as its thought through.
Cheers
Chris Crombie