I've raced an 02' Rubicon (499cc) and I beat it easy. I also raced our Rincon and didn't loose by more than 2-3 lengths. It didn't start pulling until I was in 3rd gear or so.
However, I raced the POS 660 Grizzly on just 27's and beat it both from a dead stop and a 3rd gear roll. 660's were the worst bikes ever made by Yamaha in my opinion.