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.