This is what I mean when I say I'm not sure if you're actually interested in the answer. The Wikipedia article is a pretty thorough treatment. This isn't some new or unexplored area, it is about as well trodden ground as the economists have. There isn't any need to gather more evidence to retest it yet again, the numbers are well known.

The income-maximising tax rate is between 60 and 75% and depends a bit on local conditions (probably mostly migration and language barriers). Lots of places have gone beyond it, happens all the time, and they generally lower their tax rates when someone points out they could make more money that way. You'd probably find the California tax people do studies on this sort of thing fairly regularly; not that anyone particularly cares or that I'm going to try and look it up. The real question is whether the government should even be trying to maximise the tax take.