The 6xx come with considerable enhancements over the 5xx, and 64-bit isn't even one of them. The 5xx were 64-bit, I have even said that Intel have sold more EM64T Processors in the first fourish months (not up to now, up to the point CNet said it) they have been available than AMD have sold 64-bit Processors in the entire 18 or so Months.
The 6xx, the EE I'm working on of course that's the only thoroughly released set of stats, the others all have numbers the EE is more precise has 1066Mhz Bus, 2Megs L2 Cache, Cooling Enhancements and works at 3.73Ghz.
And seriously; even an extra 20 Watts requirement is not going to make you need a PSU Upgrade, or indeed get noticable ups in your Electricity Bill. A Fan is a fan, and until you get Watercooling you're going to hear it; its natural for a Computer and I don't think anybody cares about the sound as most would have Music on.
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.