When I was overclocking with my Crucial Ballistx I was 1:1 with PL13, then best I could tighten upto on that was PL10 but took a e load more voltage across the board, so I settled for PL12 in the end.

But now with this new kit im running 5:6 and like I said earlier, I got nothing but erros PL10 and above, the last thing I expected was it to be stable at PL8, memtest Pro is just comming upto 1000%, I shall prolly leave that running overnight too be sure and then work on increasing the overall mem speed, after all 20mhz extra is sod all.