daveinva - I found the large fit me quite comfortably (maybe slightly loose), when I almost always take a medium - including a quest/rf-1100 etc. So I agree, the sizing on the GT-Air is just a bit different. Not enough to really recommend going up or down a size right off the bat - but just be aware that it's a little tighter than what I've seen from Shoei in the past.
Here's a little follow up video with my initial thoughts/impressions after putting some miles on the GT-Air. If anyone else has any questions we are happy to help!