It was on one particular contract for that period about a year before I went to work at my present startup company.

It was crazy I'll admit, I'm unlikely to want to do that kind of compressed work schedule again.

I actually didn't see daylight for most of that time and ran mostly on something I think was an adrenaline high. The sense of accomplishment at the end of it was enormous.

It was a crazy rewarding experience both in terms of self-satisfaction and in the wallet. I made a year's salary + about another 20% in bonus pay + a few other interesting compensation pieces.

More importantly, for that 12 month work year I managed to accrue the equivalent of 2.5 years of experience by hours and in terms of total output with that contract and some other long hour work, likely more since I had 100% focus on that work with absolutely no room for interruption, it's had a amazing impact on my career trajectory because I can point to that remarkable output and all of the spin-off developments that came from that body of work. In addition, I probably learned more in that 4 months that I had in my previous 4 years of work. It also landed me my current position as employee #(some single digit) with my company and put me immediately into a position of significant responsibility.

It's also given me good perspective on how much I'm worth when negotiating salary as well as how abysmally few hours are in a 9-5 40 hour week and how little work I can get done in that time by comparison.

I wouldn't recommend it for most people though, it was a pretty big sacrifice, but I'd wager that if I were to become employee #0 and startup my own company with my own $$$'s I'd work about those hours to see it off the ground.