The 7.3 has aluminum or something and the 7.2 is steel. The 7.5 is CF. The manager at the shop is a neighbor of mine and he agreed that if I was going to be riding a good amount, I should get the 7.5 if I had the money. I don't think he'd steer me wrong . . . hopefully.
Chibi - I just noticed you're in VA too. I'm in northern VA and ride on the W&OD trail.