DDR550+ on s754?

[mavalpha]

How much voltage do you guys have running through the CPU and chipset, those of you that are running obscenely high speeds on the RAM? I realize that numbers vary, but here's what I've tried so far:

3400+ Newcastle 0441, up to 1.85V (yes, I've gone all the way up to 1.85!)
1.8V NB
270x10=2.7GHz, DDR540. I run it 2.7 without problems, but 1.75V on 225x12.
My RAM is good, and my processor can almost make it. The only problem is that in the transition from test#5 to test#6 in MemTest86+ 1.55 (built into DFI NF3 BIOS), I keep turning up errors- often hundreds of them, and always listed as #5, but at the very end! If I run #5 alone, it'll pass without any problems; the same holds true for #6. The transition is what kills it.
I've just about given up and admitted- though not accepted- that my memory controller craps at around 260MHz- damn CG! I WANT NEWARK!

Even funnier part:
I started testing at high voltages (like 1.85V), and it gets really interesting; halfway through test#4, my computer shuts down- kaput! My UPS goes haywire at this point, and needs to be shut down and reset. My monitor is fine on the same UPS, as are my USB hub, speakers and external sound card. My PSU is a ModStream520, and my UPS is an CyberPower 825AVR- about a year old. It doesn't matter what kind of RAM I use, as I've tried with two 512MB sticks each of BH-5 and OCZ 3700EB- always one stick at a time.
I tried lessening the power draw, so my video card is just a GeForce4 Ti4200- all hard drives and opticals are unplugged.

 

[baldrik]

more than likely, its the on die memory controller on the processor. lots of A64s can do higher mhz than the memory controller can handle. like mine for example..my cpu tops out at just under 2500mhz(250x10), but the mem controller tops out at 228mhz, so i run a divider that puts my ram at 204mhz and my cpu at 2450(245x10).