I'd suggest removing all ram but any like chips (2x256 ocz) and start with those first in dual channel mode. Most likely the others will only hinder you.
I'm guessing you meant prime95 and memtest. Both are fine to test stability. I'm not sure if your cpu is locked or not, but try to underclock it (yes, underclock) and use memtest to isolate the memory. Anytime you can remove a variable from what might be causing instability you'll get to your final destination sooner (hence, removing generic ram from the equation).
I can guide you further probably, but I'd/(we) would like to know what mobo you have and maybe power supply too. Add it to your signature also.
-LxOxSxI