Just because a stock car runs stock figures on a dyno, doesn't always mean that the dyno is bang-on accurate.. I have lost count of the RR days I have been on and seen stock figures from a stock car and then laughable ones from a modded one..
I am with you RR with regards having a 'more realistic' figure for your car rather than the highest you can possibly get (regardless of how accurate it is).. But JKM is renowned for giving the lowest in the land for modded VAG cars on RR days. Isn't the highest Stage 2+ K04 car that has been run there still only 330bhp for example?
Also - call me cynical, but I have never known a RR venue find so many faults with cars that are run on their rollers..
Also agree that the best way to record gains/losses/general heath of your car is to run it on the same rollers each time.. Best way by far.