Well, I think the 2*512mb pairs of OCZ VX might be better overclockable then the BH-5 pairs of 2*512mb

The difference between OCZ VX and BH-5 is more in the fact that some 256mb BH-5 sticks have done 300mhz 2-2-2-5 and there is no way OCZ VX can beat that.
Maybe the OCZ will clock a bit higher with the new ATI chipset, how knows what will happen?

I'm thinking of buying a 2*512mb pair of OCZ VX for my new system but I'm not really sure if that would help allot sind I allready have some Corsair XMS PRO PC4000 that can do 260mhz at 2.5-3-3-7

Well if my new system wil be an FX-53 or FX-55 I think I might just by a pair of OCZ VX but if my new system is going to be a Pentium-M Dothan I'll stick with my XMS.