2.4-2.6 GHz seems to be the limit on E6 Palermos. XBitLabs got a 3400+ to 2.6 GHz. I got my 2800+ to 2.4 GHz. I think you're very lucky to have passed 2.4 GHz, and I don't think your RAM is holding you back. Anyway, all you can reasonably squeeze out of it is another 200 MHz or so, and that's probably not worth the risk and/or trouble.
Nice job, though!