Honestly, an
Antec TruePower TP-750 750W Continuous Power will be enough for a dual 6950 setup, assuming you flash them to a 6970. A Crossfire 6970 system uses only about 550W (not just the cards, the whole system). This leaves you with plenty of room for other upgrades and overclocking because just like the Corsair HX, the Antec True power is a high quality PSU that will have no problem delivering up to 750W of continuous power.
One of the major reasons I would recommend an i5 build over AMD hexa cores is because Intel's turbo boost is leaps and bounds ahead of AMD. Intel's turbo boost kicks in whenever you need it, regardless of how many cores you are using. The extra clock speed boost depends on your system temps, and not how many cores you are putting the load on. AMD's turbo boost on the other hand only works when you are using 3 cores or less, and it is a static increase of only (up to) 500MHz.
The other reason is that Intel i5 2500k is
at least 30-50% faster in games than AMD's hexa cores. Best of all, it costs roughly the same as the AMD build you are looking at.
If you are primarily going to use your rig for gaming, then why sacrifice so much gaming power in hopes that games will start using more than 4 cores? In 3-5 years they might, but as of right now, most of them use 2, maybe 3 cores.
---------- Post added 2011-03-04 at 09:36 PM ----------
The extra $30 or so is worth it if you are planning to flash it to a 6970. If not, go with the 1GB version or a 560TI, but just remember that you cannot flash the 1GB version.