> btw mobo is Asus P5Q3 S775 P45 with the Intel E8500 CPU
The P5Q3 requires DDR3, not DDR2:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131298
(DDR3 2000(O.C) / 1600)
Start out by leaving the memory settings on AUTO in the BIOS
for the DDR3 version of Corsair's Dominator line:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=1052315794%201052429371&Description=Corsair%20Dominator%20DDR3&name=DDR3%201600%20%28PC3%2012800%29
Then, change the FSB to 400 MHz and enable SpeedStep.
Download & install CPU-Z to confirm that your chipset
has chosen a 1 : 1 FSB : DRAM ratio. CPU-Z will also
tell you what SPD options are available with the RAM
that you do purchase. "SPD" = Serial Presence Detect
which is a special chip on the DIMMs which permits
automatic BIOS configuration of RAM with SPD support.
If the memory you buy can clock higher, then
you can try an FSB : DRAM ratio of 1 : 2
(i.e. 400 MHz FSB and 800 MHz DRAM)
With that CPU you should see an automatic overclock
with SpeedStep enabled.
With these settings resulting in a stable system,
you can then try to push your overclocks even more,
depending on your skill and willingness to experiment.
p.s. The comments above concerning the P35 chipset
and DDR2 Dominator RAM are off-point, because the P5Q3
motherboard has a P45 chipset and it requires DDR3 RAM.
MRFS