Ghislain is right. The G'byte G31/G41 boards are great for CPU's with a low FSB and high internal multipliers such as the E5200 family. They are not so good with CPU chips with higher FSB's.
The next thing is that you are overclocking your RAM and that may be limiting your OC. Set your memory clock so that it is twice the FSB.
Third thing is, you may just have reached the limits of your particular CPU chip.