v_1matst:er... what's wrong with air? Nitrox is great and everything as a tool to do 'longer', shallower dives but air works just fine... even deeper than you're limited to on whatever mix of nitrox you are using....
Bigger tanks will help you out even more than nitrox if you want to be first in, last out... assuming your buddy is 'last out' with you. Give me a PST e-7 100 filled with air and I'll stay down all day.
here here...