Compare:
http://ark.intel.com/compare/33924,35428,33921
The only real difference is that the QX is older and uses more power. Just about everything else is identical.
As for gaming, it will probably struggle in new games. I have a Q9550 @3.5ghz and it can handle Starcraft 2 at medium/high settings. But I wouldn't try anything major on it (i.e. Forza horizon 3).
The socket 775 died about 9 years ago, but the CPU's are still viable for some things. However, finding a q9650 on eBay for a decent price is rare. You could save money and get the q9550 like I did and OC it. From it's base of 2.83ghz to that of the q9650 of 3.00ghz is a mild OC. The Core 2 Quads had a great reputation for overclocking. I got my Q9550 for $40 used on eBay...