Aaroona: Ahh okay. that makes sense!
Cheers for the info guys...
So Im running at 1648.6Mhz
My CPU is over clocked to 4.3Ghz as well, from stock 3.4. Turns out the MB has got it so you can select "Power mode" or something, and it will overclock your CPU and have your RAM running at the quickest speed it can. So that's handy, I've been running at full speed since day 1 when I changed it :)
out of interest are you running auto or manual overclock?
I note in docs for P8Z68 Asus that 4.3 was auto outcome but they were going above 5 with no issues?