CPUZ says that your FSB:RAM ratio is 3:5. You are overclocking your RAM. And that is limiting your CPU overclock.
Go into your BIOS and take the memory settings off Auto. You need to set your memory clock so that the BIOS indicates that it is twice the FSB freq. That will set your FSB:RAM ratio to 1:1. You should be able to push the CPU freq a little higher.
Overclocking RAM, particularly in a Core2 system does little to improve performance.
In BIOS for RAM i can only set the index freq 533 667 or 800 and the timing...and i don't have cpu : ram ratio to change