RM sizing chart?

Haven't seen a chart either, but....

I'm 5'8 and ride a 16.5" '02 slayer and it's a great fit. I've sat on and rode many other 18" bikes and they've all felt pretty big.

I don't think I've ever seen a body fit chart on Rocky's website. You could use other manufacturer's sizing charts, but you want to compare horiz top tube length, not seat tube height.

On something like a long travel suspension bike you really want to test ride frames in the size range to see how the suspension and your body mass distribution works together. Even the basic guideline of long leg/short torso versus long torso/short legs doesn't cover the dynamics of where your centre of mass is. And the centre of mass and the bike's dynamic centre will interact with each other. Some people like a short top tube so they can get up on the bars and some people like to have a longer top tube so they can keep their weight further back. So try a 16.5 and an 18 and see which one works best.