from LegitReviews.com had a chance to play around with Kingston's HyperX DDR3 4GB 2133MHz kit, or as they like to call it, "an insane HyperX T1 memory kit". Despite the fact that this one is rated at 2133MHz at CL8 with 1.65V of voltage, LegitReviews managed to hit a stunning 2.4GHz at CL9 with just 1.75Volts.
The kit is capable of hitting 2350MHz without voltage adjustments but at looser 9-9-9-24 latencies. If you in any case want to run it at 2.4GHz and probably beyond, you have to give 1.75V to memory and a bit more to QPI, 1.35V to be precise. Bear in mind that both of these results were done at 1T command rate.
The bad side of the story is that this one has an MSRP of US $379 which is far too much for a dual-channel 4GB DDR3 kit, but then again, this is the fastest DDR3 kit around and premium products always had a premium price.
You can check out the review here