you are only running DDR2 800 with those sticks @ 5-5-5 so your not taking any advantage of them since they should be running 1066 5-5-5
and
you may find out because you are using 4 sticks @ 1066 the system raises their timing to 6-6-6... and... you can be unstable with 4 sticks @ 1066 5-5-5 so there is a lot to consider because of the 4 sticks.
I would probably set the clock up with 2 sticks and then install the other 2 in order to see if timing and stability remain the same