I have a medium in the Arcteryx Gamma MX...
I have a medium in the Arcteryx Gamma MX and it fits well if bit snug. From what I'm reading below, someone 5'10" 180 needs a large? Is that accurate?
Yes, I would suggest going for the large.
Actually, I am sitting here wearing my 2010 sharp point, and have my 2010 gamma mx a foot away from me. I happen to be 5'10 180lbs exactly, but I bet you have already bought something by now. However, maybe this will help someone. Anyway, I have a med in both, and would not recommend going any bigger. the sharp point runs a little bigger than the gamma mx, but it is only 2 way stretch, and significantly burlier so you sort of need the extra size to be able to move as freely. I ski in the sharp point and probably would have torn my mx to shreds if I used it instead, but the sharp point is doing fine. It layers good enough, but you can wear it around town with a motorcycle jacket form fit look at the same time. It dose a great job of blocking the wind, and the velcro cuffs are SOOOO much better than the mx elastic ones that I think I wear the Sharp point over the arcteryx just so I dont have to fight to see my watch some times. However, I still have a soft spot for the Gamma, and grab it for climbing, and about everything else I do. Both are PIMP and top end awesome, good luck.