I find that it can be really difficult to measure productivity some times, especially when long hours are involved. If I work 2x hours and I get stuff done all throughout that time (beginning, middle, and end) then I'll tend to think all of those hours were well spent. But when I spend the time and effort to really look at productivity I find that typically spending more hours only produces the illusion of greater productivity. Often times I'll easily forget the downsides of working more hours, such as poorer quality of work, less focus and ability to concentrate, more down time between periods of work, greater likelihood of being OK with partial or inferior solutions, etc.
Over time I've come to the conclusion that except for "it's broken, and time is money" or "I've found inspiration at midnight" situations it's pretty much never a good idea to consistently work long hours on software projects. It's better to work smarter and more efficiently and to have the resources available to do big refactoring / redesign / performance improvement projects when necessary than to just work flat out and always be in an "ok, that's good enough, moving on" state of mind.