Stuck at 2.68

For the last couple weeks I have been overclocking my 4600 to try and find its max. The highest I have reached so far is 2.68 @ (223x12) with 1.376v. My RAM is also now running at 446mhz or 892mhz. I haven't played to much with the RAM so I don't know if slowing it down will help. As soon as I bump to 224x12 it fails Prime 95 within the 1st 5 hours of testing. I did increase the voltage once to the next level but it did not seem to help. Any suggestions....I would really like to hit 2.7 or higher if possible.

-My 4600 is the 90nm int the F family with a stepping of 2