the gigabyte ga-ma770-ud3 motherboard is an AM2+ motherboard that supports 1200MHz DDR2 ram but only with certain compatible processors... which processors support this RAM? is it just the AM3 processors or can the phenom II x4 940 AM2+ processor work with this speed of DDR2?
More aboutma770 memory support
There is no earthly benefit to running DDR2 at 1200, especially considering the price differential, and lots of 'gotcha's lurking in the weeds. Stick with 1066 max - you still may only be able to run two DIMMs at that speed...