I found the info out on the GM Racing website from Ralf Hellbing himself, then i decided to conduct my own tests and they are the results.
If you wire up the cap and drive wiht a very low turn motor you can visibly see the difference. Obviously it will depend on how good your batteries are but there is a definite drop in voltage when you get on the gas.
I found when i went much above 10,000 the voltaged drop did not change that much as the cap cannot deliver that much current in a small period of time.
As for stock racing, I don't think it makes as much of a difference but it does make some difference.