See here for my comments on my Girlfriends one: http://www.singletrackworld.com/reviews/yeti-asr-5/
She is 5'11" (and a bit apparently) with 34" inside leg and she is on a Medium with a 70mm stem, and a slight layback post (KS i900r). Seems to fit well. Large would be far to big.
As for the ride, personally I am in the camp of the bike doesn't matter that much, as it how much you ride that counts ..... However since getting this bike, she is significantly faster on the climbs (was out on the Quantocks last week, and at the end of the day she commented on how she hadn't used, or needed the granny once) and is now fast enough to heckle people to go faster on the descents, who she was previously happy just to keep up with.
So the comments on, its a bike that will hurt you seem to be quite accurate. As it will kill you on the climbs by tearing your legs off, and kill you on the descents by encouraging you to go that little bit faster.