first things first-- never think that endurance geometry = slow. plenty of endurance bikes are quite fast and light. they're just designed around different goals.


anyway--

sure you can use either bike and modify the bar height. pros do it often because they don't get that many frames to pick from and even a man like Cavendish doesn't get to pick which brand of bike the team uses.

CVV's Cervelo R3:


LA's Trek Madone 6.9 (2009):



Also note that going up or down a size from normal changes the HT height a lot. Lance is on a 58cm frame at 5'9" ... if he were on a 56 or smaller, he would need spacers and/or positive stem angle to get that bar height.