Ok. Thanks for the update. Your RAM is rated at 1066Mhz, great speed for DDR2 era. OCZ was great for me back then as well. They got bought out by Toshiba years back though. If you didn't adjust the DRAM divider, you would be at 720Mhz RAM. In other words, you could keep same divider, or adjust RAM to faster. You can't access EPP profile, you need Nvidia chipset board for that, but that's another story. Be aware that if you increase RAM speed, you would have to loosen timings.
Also, what cooler are you using? Good mounting? Cleaned of dust? Fresh thermal compound? If you want to go further, a cheap replacement could get you to a much higher OC if budget allows.