Looking at the comp wheel dif tells u this.I guess I should have worded it differently.they both have their pluses and minuses.in my personal opinion the 851is better.to others the 500 series is better cause of weight difference. I'm not trying to cause a stir here just giving my opinion.
I've got buddies with s510s.
One of the best things about the 851 is nobody really runs them yet. Everyone and their uncle has a 500 series. Lol.I like being different.