Both have plenty of power for the trails I ride on. I bought the 750 over the 500 for 3 reasons.
1. Larger engine wouldn't have to work as hard
2. It was only a few hundred dollars more ($3-500)
3. Readily available
I would have been fine with either one though. These bikes are very wide for "tight trails" & you'll probably have lots of pin stripping. A sporty 2wd model may be more fun than these utility models.
i have both the 750(mine) and the 500(wife). both are identical other than engine.The 750 of course, has more grunt and good response.Honestly, though, each machine can follow the other anywhere we go when riding. we've been in the sand dunes, mudding , and pure trail riding. at the end of the day, you wont go wrong with either.