Me too...... 5'7" and 160......what a ride. At first the big 5 seems quite the "reach" yet once you spend time on it.....no problem. My bike is stock and all I needed to do was set the sag properly for my weight and all was fine. Starting the bike took a little practice too and took me a while to master. Starting requires managing the bike on the tips of the toes.
For the smaller rider, who can learn to ride the 500, you can easily loft the bike and really clear the jumps. The bike really gives the rider a lot of confidence (maybe too much) if you respect the power. I ride mine like a four stroke when needed and spend most of the time in 2nd or 3rd during practice on the track.
I love the bike. Just to give you an idea of how manageable the bike is, after 20 years being off a dirt bike (my last bike was a Maico 400!) by the end of my FIRST day back at it, I was clearing 20 foot table-tops!
What a rush. It all came back, must have good muscle memory or must be insane.
So, stand on the tips of your toes and go for it.