Level top tubes, and with the crazy left over XO-1 frames used to build up XO-3 bikes in 1994, well you can't even make the blanket statement that the XO-1 or 2 are the only ones with real BOB appeal.
I saw a fellow last spring, while riding in the Diabetes charity ride, who was given a 94 XO-3 by a lady as he was going door to door trying to line up pledges. She told him she had no money to make a pledge, but she had an old bike in the garage he could have. It looked like it had less then 100 total miles on it (counting the 30 or so that day). I was on my XO-2 and I was startled to see a bike with mustache bars and the same green color-- Struck up a conversation and got to hear his fortunate bike tale.