Well, I spent about an hour on a lengthy reply but it got erased so here's a condensed version:

The 17" with a 90mm stem actually has a longer cockpit than the 19" with a 60mm stem by around 15mm. So I was wondering if your "cramped" feeling on the 17" is more due to your legs in relationship to the BB.

I'm 6'1 1/2" and I have a 34" inseam. I origionally built my 19" with an Easton EA50 105 x 6 deg rise. I came from a Gary Fisher XC hardtail so when I rode the Jamis, I felt cramped. When I spent time on the Jamis and moved back to the Fisher, I felt overly s-t-r-e-t-c-h-e-d out. I sold the Fisher to upgrade the XLT and never felt better. I actually switched to an even shorter Thomson X4 90mm x 0 deg stem. I feel much more comfortable on the XLT especially in the fast/tech sections. One thing I DO miss about the Fisher is being able to lock out the front end, stand up on the pedals and muscle up the long gradual climbs. Now I have to sit and spin. I don't get up the hills quicker...quite the opposite actually, but I make it up on the DH and technical sections.

You coming from an XC background may feel wierd for a while, but once you're used to the tighter cockpit...you'll attack things that you used to pansy your way through. I think a longer 115mm stem won't muck up the handling too much, but I really prefer my 90mm.

Any LBS worth their weight would let you try out a number of stems to see what you like best. If you would prefer, I can ship you my EA50 105mm x 6 degree to try out on the trail for a while. If you like it, you can buy one from your LBS and ship mine back to me...but seriously, your LBS should be able to do this w/o you and I paying s&h. Either way, I just want you to be satisfied with your XLT like me.

I also installed a Thomson layback on mine...that combined with the ample rail clearance of the WTB Rocket V Team Ti has given me ample room for leg power and a good feel in the cockpit. Mind you, I'm using an Easton eA70 HiRise bar cut to 25" so I'm probably a little more upright by 1/2" or so.

The biggest thing is that for aggr. trail riding...a 17" bike should be perfect for you at 5'9". If you were going XC racing...you could probably bump up to a 19", but I'd still say that anyone with your build should be on a 17".

My $0.02