seiichi,
I actually run my E6300 full time OC'd at 333FSB on my P5B-Dlx. I run the RAM 1:1 (DDR2-667) and I've actually undervolted my Vcore to keep temps down (1.20V, 36C idle, 48C load). I ran prime95 torture overnight to check stability and its good with these specs. I've never had a stability issue in the 4 months of running this way. Keep in mind that each component is different and you may not be able to duplicate these settings. I'm using an aftermarket cooler as well. As ronin27 said, leave your multiplier at 7.