In my experience, the RGV can be made to go extremely quick, but not for any length of time. Since the RS uses that engine, I'd guess they would suffer accordingly if highly tuned.

Must admit, only ever saw one racing, and it wasn't particularly fast. I think people opt for the RGV as bits are easier to find and it costs less when you crash!
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball