My brother-in-law has an 05 Rubicon and it smokes my 500 Foreman S. Top-end I can usually keep up but the Rubicon accelerates through the gears so much quicker. So far he's been very happy with it. However, shortly after purcasing it an angle sensor went bad. Honda took care of it obviously so the only downfall was being without it for a few days. I've heard of similar problems with quite a few Rubicons as well. I'm not sure how the ES would match up to the Rubicon as far as MPH goes. With the larger motor I'm sure the Rubicon would be slightly quicker. Tough decision, guess it depends on what you're looking for. There are some obvious differences such liquid cooled/air cooled, fully automatic, and price! Just my 2 cents...