I'm 6'3" 185' and picked up a Stash in the large last week. Took it out for some hiking in the snow a couple days ago and skiing yesterday. Pretty cool but 5 stars for value. The sleeves run long and the fit is very athletic (which as a tall slender guy is great). As to length, the large drops 7 inches below my hip bone and the sleeves a couple inches past my wrist.
If you want 'really long' over the butt for skiing in heavy pow it looks like the 'bombshell' jacket is designed along those lines (removable powder skirt, etc.) and I'm guessing will be a little longer in length (I might have to order one to find out - and go with an XL for layering). But for an athletic fit in a technical, multi-use shell (climbing, hiking, backpacking, etc.) this is a great piece and a solid value.
Some other thoughts: I really like the material, comfortable to wear and soft to the touch, very breathable for a shell and packable. The phone pocket with 'audio out' is a nice bonus. I've a $370 TNF jacket that doesn't give me as much. Only question I have is how waterproof the fabric will be in a downpour - though for light precipitation and Wasatch snow - I think the Stash will do just fine.
Last note: the hood is 'form-fit'- not designed to fit over a climbing, biking or skiing helmet.