I needed 1.28v for 3.2Ghz back in the day for my E6750.
Add +0.2 on the NB over stock and increase the CPU VTT to 1.35v and see where that leads you.
You're also probably crashing because you're trying to run CAS 4 at 750Mhz, not to mention with different sticks.
Try 18.104.22.168. I bet you'll be able to get 400Mhz with a multi of 8 for 3.2Ghz and a nice round 800Mhz on the rams.
From there on, up the NB freq until it crashes, up the NB voltage and core voltage and if none help, up the VTT voltage as well and see where that gets you.
Don't go over 1.45v for the CPU, VTT or 1.5v for NB. Keep the case as ventilated as possible.
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