Having trouble overclocking Skulltrail beyond ~360FSB...

I haven't actually tested 361-368 exactly, but I have been able to boot at 360. I've tried 369, 370, 380, 399 and 400 with no luck. It usually halts at BIOS code 12 before the screen initializes. I'm running the system in my sig:

2x Xeon E5420 (1333 FSB, 2.5GHz; tried at 1.25V to 1.35V)
2x Kingwin Direct Touch heatsinks with 120x38mm Ultra Kazes
4x2GB FB-DIMM DDR2-800 (tried 1.96V and 2.00V, with AMB at 1.5V)

Tried MCH and FSB at 1.35V. And I've also put the RAM to 6-6-6-18 1:1 for the sake of eliminating that as the problem. Even tried 5:4 to lower the RAM, still no go. Edit: Just tried it at 7x instead of 7.5x, still nothing! Also bumped MCH to 1.4V. Maybe the newer BIOS sucks?

I have not touched the GTL REF settings, and the two other CPU voltage options are left as disabled. I have tried enabling them, to no success -- still won't boot at 370. Spread spectrum for PCIe is disabled. PCI latency is at 32. C1E and EIST are off, from what the BIOS tells me at least. VT and VT Turbo or whatever it is are both enabled.

What have I missed? Help me XtremeSystems, you're my only hope.

Edit 2: Everything back at default, I can boot at 365 FSB. There's no way it can just plain fail at just a 4 FSB increase from that! Going to try another BIOS. Edit 3: Okay, 365 doesn't seem to be stable at stock volts, but I got into Windows. I turned up the volts and it didn't even get that far! Down to 361...

Running the CPUs on water now, and I mounted a fan on the DIMMs -- still can't get past this wall. Is it a BIOS limitation?

I've even tried running the memory at 5:4 instead of 1:1, so that the memory runs at 667 while the CPU would be at 400. Even running the memory at 6-6-6-18 timings and the voltage bumped up to 1.96V. Still stuck at 360 FSB. I have tried the 1149 BIOS, and I just switched to 1140 and still no luck.

Something isn't right. My FSB is stable at 419. I've seen mention of folks not being able to get above 420.