The big thing to remember is that all that O2 you lose on the way up is O2 you will get back on the way down. You don't want to be completely spent at the turnaround, but you should be giving a pretty damn good effort.
This is one race where you will encounter every other racer. The fast and the slow, you will deal with all of them.
The few goals on the way down: Stay focused, stay hyrdated, and stay upright.