Performance at varying timings
Overclocking analysis was carried out by using 3 sets of memory timings; 2-2-2-5 1T, 2-3-2-6 1T, and 2.5-4-4-8 2T. Load voltage was set to the EPoX 9NDA3+'s maximum, which amounted to around 2.68v.
The tightest settings sees Corsair's XMS4400 crawl over the DDR400 barrier. Using an educated guess, I reckon Corsair's tweaked the PCB to offer sky-high clocks at the expense of ultra-tight latencies. Still, hard to argue with RAM that can also run at DDR400 at 2-2-2-5 1T.
Relaxing timings to 2-3-2-6 1T (TRCD=3) gives slightly more frequency headroom. Again, the very fact that the modules are engineered for maximum MHz explains why this TwinX pack isn't quite able to match sets from OCZ and Crucial that use similar ICs.
282MHz, or DDR564, is limited by the test motherboard's clock ceiling and not by the Corsair modules. It's gratifying to see the TwinX4400 pack run in excess of default speeds with almost 0.1v less juice than recommended by Corsair.