That's a handy formula. Basically I was primarily interested in that efficiency component, and how much that actually changes with conditioning. From more detailed searching I see it's almost always in 21-23% range among trained cyclists.

On a side note, I just got a V02 max test today as part of a medical study and reached exhaustion at 450 watts, after about 15 minutes of ramping up. I couldn't imagine holding that for an hour! I was in a world of hurt! For me, 'failure' at that point would definitely be the right term!