I just got one with the 5900 bag a couple weeks ago.
Although I have and like my exo 3500, I sold a kifaru and thought I'd try the SG, the frame seems to fit my curved back very well. I played around with it a bit but have not packed any heavy loads yet, but it seeks like a great setup thus far.
Here's a link to a Rokslide post.
http://www.rokslide.com/forums/backpacks/59201-stone-glacier-xcurve-sky-5900-field-report.html
