hi there,
found this thread through a google search.
i'm in the same boat. i have an MSI P6N Diamond which supports the memory speeds, but i too have 4 x 1GB sticks of Corsair XMS memory 1066 but only runs at 800MHz.
i've manually changed the timings to 1066 and upped the DRAM voltage to 2.1 (suggested voltage) and Windows will load and run, but will freeze up on me about 5 minutes into it.
my friend, (who's probably not the best person to cite sources) says that it can't be done to run at those timings and it will always downclock to 800Mhz.
i've picked up the same kit, only this tme it's a 2 x 2GB kit and hopefully this will fix it. i'll let you all know how it turns out.
*if you're running a 32-bit OS (i'm running Windows Vista Ultimate-32bit), you will notice that it's only utilizing 3.0GBs. with a 2x2GB setup, you'll be able to utilize a bit more up to 3.5GBs. i'm hoping this will correct my situation and run at the desired timings