dfi lanparty ut ram overclocking problems

[spaceheater184]

does anyone have any advice on settings for using more than one double rank stick of memory (i.e. 2x512, 2x1024)? i am using 2x256 pdp tccd sticks right now and i can get a huge overclock of 301MHz 1:1 on my machine, but my friend, with largely the same system except that he has 2x512 pdp tccd sticks and he can't even get 250 stable. his dram settings are the exact same as mine right now, but i think that may be the problem. any help would be appreciated.