a lot of ddr2 800 kits will hit 1066 with 4-4-4-12 or lower, my ram does.
-but- a lot of 1066 kits will hit 1200+ with 5-5-5-15, my ram wont.
if you are planning on going over 525-550 fsb (i dont know what that mobo is capable of) with a 1:1 ratio the 1066 will be better.
as luke said...if you are not going to oc or oc to 450-500 the 800 will probably be fine. you can almost always raise the timings to 5-5-5-15 on ddr2 800 and get that speed, unless you get some lemons.
I'm noticing this question getting asked over and over again....
and there are not... from what I'm seeing (the RAM question)