Go for the 800 if your going to overclock.It will be less work then underclocking the
ram.If your not overclocking go for the 1066.The Abit motherboard only supports DDR2 800mhz and so if you want 1066mhz DDR2 get the Gigabyte.But remember you can always overclock the 800mhz on the gigabyte to 1066mhz.