The differences are as follows:
965 is newer so it has had some improvements made. It looks like it will be the winner between the two WHEN NOT USING CROSSFIRE/SLI. (as it apparently has its fair share memory controller tweaks) It has the ICH8 southbridge as well as native support for DDR2-800. It however does not have an optimal pci-express lane setup. It is 16x/4x instead of the ideal 8x/8x or 16x/16x thus it is rumored that ATI will not be making Crossfire available for it. Not that a person with a little creativity couldn't circumvent that restriction.

We don't know anything about the overclockability but by nature I would say the 965x SHOULD overclock better, however reality may be alot different. The 965 is not being marketed as the enthusiast chipset, so therefore many motherboard manufactures will not market 965x motherboards as enthusiast motherboards. If that is the case then we will probably see 975X overclocking higher.

I would not put 3.5-3.6ish out of range, the Asus offerings are looking very nice and I'm sure alot of companies will be putting out more than decent clocking motherboards.