Update:
Prime (blend) stable @ 45x.
I only mentioned briefly that I was running my RAM @ XMP.
F3-17000CL9D-4GBXL (2x2gb sticks)
Well, I had thought the RAM was stable but it wasn't. Switching it back to 1600mhz (auto), and the system is perfect @ 45x with 1.36v (I can't believe I was trying 1.4v earlier for a mere 45x). The vcore might even work lower...
Very good info on spread spectrum btw. I'd read about it elsewhere but I don't think it ever made much sense to me until now.

So now I have two problems:
- I am fine staying @ 45x, but I want to be able to run my RAM at XMP settings. G.Skill "guarantees" those settings AFAIK, but XMP causes instability when the system is OCed @45x. I've tried various combinations of voltages without luck so far. Ket, your post on voltage ranges is invaluable for me (you did post that earlier). I was also thinking that high VTT was better for RAM than PLL, very good info. Any other recommendations?

- I do indeed have a 45x wall; attempting to boot @ 46x causes black screen after POST. Falkentyne, I was dismissive when it came to your idea about PLL Overvolt, but now I'm definitely open to the possibility. For the record, PLL overvolt on or off makes no difference up to 45x (can boot into Windows just fine, system stable without it). Just can't boot to 46x. Seeing that other people have no problem with 48x at low voltages, I'm left scratching my head here... It's weird because 45x is Prime & IBT stable...why would such a small jump in multi be impossible?