OC Q9650
OC Q9650
Whatever the CPU needs to accomplish. It won't be a fixed solution, each CPU is unique. You must also keep an eye on temperature when increasing voltage. Staying stable is important, but running the CPU at high temperatures can reduce its lifespan.
Not used to gigabytes but my old Q9650/ASUS P5Q-PRO would start up in Windows at an extremely low VCore. You should try the same, beginning under 1.0 and increasing VCore until it boots, then stress test by raising VCore until stability is achieved.
The Gigabyte boards were quite effective overclockers from what I recall.