Can Gigabyte GA-M720-US3 work with 1066 modules?

1066 is VERY hard to achieve on an AMD platform. It basically has to do with the AMD memory controller found on the CPU. Some boards can run fine @ 1066 and most can't. I have a board that supports 1066Mhz but when I raise the voltage to 2.1/2.2v it crashes no matter what timings/settings I have. My suggestion is try and lower your timings to 4-4-4-12 and lower your frequency to 400 instead of 533 and try to boot. Also remember to lower your voltage to at least 1.9v. If it boots and you are stable then you are actually running at a faster speed due to tighter timings. If you crash, then raise timings to 5-5-5-15 and leave everything else the same.

My board is faster running my ram at 4-4-4-12 (800Mhz) as opposed to 5-5-5-15 (1066Mhz).

glad it worked out for you....