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Ah, right.
Using RAMs from different manufacturers usually forces other sticks to follow the speed (and timings) of the slowest one.
It doesn't directly relate to your CPU being hard to overclock, but it's probably just too much for your mobo to handle and regulate the timings and voltage of your RAMs alone.

Well, CMIIW; haven't been too deep into OC-ing myself, hence me getting stuck on E6550's 'OC cap'.

I don't won't to post a new tread,but does plugin realese march 2010 works with 0.9.6 beta1888 ?

It should be; they won't release or endorse that plugin pack if it won't work with the publicly available 0.9.6 beta.