@CumminsPusher mentioned running out of power, and I had the same experience several times. @Montecresto recently sold his 700 for the same reason. Like him, I lived at high elevations where the 700 can struggle with really tough climbs.
Yes, the 700 rides much better...though it's still stiff due to a 1000lbs payload BUT, lessons learned with the 500 would help me if I went with the 700 again. And with a load, they ride ok anyway.
I've done a few things to the 500 now, and im much happier with it. It certainly has its moments...and things going for it. I have fun in it, and will continue to do so until the opportunity to go back to a larger machine presents itself.
That said, starting fresh with a brand new machine, between the 2 of them, I can't see ever taking the 500 over the 700 (esp the 2 seaters close price) again. If you're going with the 500, it's best to keep it on the tiny little trails it's made for. That's where it thrives.