You're going to be much better off shutting them down than hibernating. On every platform I've ever used, hibernation is fraught with problems, errors and random flakiness. If shutting the servers down over the weekend, and (more importantly) validating that they come up properly on Monday is acceptable practice for your environment, I strongly recommend that over Hibernation or Sleep.
No, you're quite unlikely to find a paper with proof, because the study would literally have to be run over the course of the hardware's lifecycle (3-5 years), and by then the article would be completely irrelevant because the model would be so out-dated as to be nearly useless for production. You could make the argument that it's a 'general study', but technology advances quickly enough that the counter-arguments of recent technology improvement are strong enough to make the entire discussion meaningless.