Overclocking the 5750 Vapor-X
To overclock the Sapphire Vapor-X 5750 all I had to do was unlock the Catalyst Control Center. The Catalyst Control Center is bundled with the driver from ATI.
The Sapphire Vapor-X comes from the factory slightly overclocked already. The ATI reference card comes at 700MHz for the GPU core and 1150MHz (4600MHz effective) for the memory clock. The Sapphire Vapor-X 5750 has a 710MHz for the GPU core and 1160MHz (4640MHz effective) for the memory clock.
I manually set the fan to 100% and slowly started increasing the GPU clock and then did the same with the Memory clock. I was able to crank the GPU core up to the maximum allowed in ATI overdrive. The memory wasn't able to be maxed out as FurMark started to artifact at 1360MHz. I was able to achieve a solid 3dMark Vantage run at 870MHz on the GPU core and 1355MHz (5420MHz effective) on the memory after running FurMark for 5 minutes.
Above was run at the default speeds of the Sapphire Vapor-X 5750.
This is the result of overclocking the Sapphire Vapor-X 5750. I have no doubt that with a different overclocking utility more could be squeezed out of this card.
Overclocking results: I was able to bring the GPU core up to 870MHz from 710MHz which is a 22.5% boost and it sure seemed like it had more to go. The Memory was able to go from 1160MHz to 1355MHz which is a 17.8% boost. Overall the overclock gave me a 19% boost in 3DMark Vantage scores!