I thought the Thraxis and UFOs fit pretty much exactly the same when I tried them. The difference between last years K2 boot sizes though was half a size off in my experience so I would be wary of ordering 2012 boots based on how the 2013 fit you in the store. I wouldn't buy boots online, but to each his own.
Thanks, it sounds like last years should be a little larger, which might be ok...I generally agree with not buying online but the cost of last year's boot vs this years is roughly a $225 difference
which is more worth the gamble to me.