both chips are 45nm and are hella OC-able. Toms did a comparo a while back, pulling 4.5GHz on air with the Q9550 and keeping up with some older i5 systems. if you're on a tight budget and willing to upgrade, you can really stretch out some of those 775 systems. that may relieve a LOT bottlenecking on the GPU but iirc will not fully clear it. with Skylake out you may be able to score some Devil's Canyon or IvyBridge stuff quite cheap, though for the most part if you're in a good position financially you might as well go for a new Skylake setup.
like what BadActor was saying, unless you're playing games that are CPU-bound you potentially could be stuck with no difference at all to the bottom line. stock setup i think is 3.1Ghz Dual core vs. 2.83Ghz Quad. 4 years ago that was a good move, now....ehhhhhh.