I was fitted for a Trek GF Paragon and was recommended a 17.5 size. The Cannondale Flash 29er 1 I was testing was a large and they have no medium in the store. My inseam is 29 and am 6'0" with big torso and short arms. I've never owned a 29er, so the Cannondale seems a bit big. Any experience/suggestions about the size I should have?

thanks,
mike