VO2 is a measurement of your maximum respiratory functionality but it's ultimate impact on performance isn't an exact science. yes, a higher respiratory capacity can mean that you have a huge engine and will rock the world (Lance), but there are studies of incredible athletes who have relatively low VO2's who also excel. I wouldn't look to it as the sole arbitor of how well you can perfrom, so many other varibales are just as important, especially in long course stuff like IM, where aerobic capacity is key.