Personally, with those as the choice, I'd go with the Q9650 and overclock it. With a lower TDP, you will have less heat to dissipate.
When i was looking at an upgrade for my legacy system, I went with the Q9550 and overclocked it to 3.5ghz. They are much cheaper on eBay than the higher models and the performance is pretty decent. Depending on the price or the QX9770 or Q9650, you might be better off getting a newer CPU. http://ark.intel.com/compare/33924,35428,34444