I bought a pair of the Pearl Izumi's from Hooper and have been happy. They provide some warmth on cold mornings (i.e. what you would expect the morning of TOU). When I wear them on runs, I can push them down to my wrists once it warms up and hardly notice the extra weight. Or you could pull a Kara and throw them off. I think mine are Med size. I'll probably wear mine at TOU and throw them at an aid station, though I would be pretty disappointed if I don't get them back- I'd rather lose a long sleeve shirt then the arm sleeves.
You can read Paul's experience with them here:
http://paul.fastrunningblog.com/blog-04-04-2009.html