OverclockingIntel's new Haswell processors come with a new graphics-overclocking-via-multiplier feature that lets you adjust the multiplier for the GPU core just like that of the multiplier for the CPU frequency on unlocked K models.
I gave this a quick try with Bioshock:
As we can see, overclocking works as intended and provides additional performance, but it is not able to turn this processor into a mean gaming machine.
I had to increase processor graphics voltage by +0.2 V to stabilize the 1.75 GHz test. Everything beyond that was not stable and crashed almost immediately.
DDR3 Memory ClockSince the integrated graphics solution does not come with its own graphics memory, the system will dynamically allocate a portion of the motherboards DDR3 to the graphics core.
The following test investigates how changing the system's RAM frequency affects rendering performance of the Intel HD Graphics 4600 solution.
As we can see, the sweet spot looks to be at 1600 MHz, which is quite cheap nowadays. If you want to spend a bit more money, 1833 MHz seems reasonable, but anything beyond that is just money spent on almost no improvement.