Broken memory divider?

It seems like one of the memory dividers (or something) is broken on my P5WD2. I didn't know this was possible...so...um...yeah.

This is what happens. I'm at 240FSB, with my memory divider set such that the RAM runs at 320MHz (640MHz DDR). Everything's fine, happy, stable, etc. at this speed (3:2 divider, right?), running at about stock voltage, 3-4-4-8, etc. The next divider selectable in the BIOS is 360MHz (720MHz DDR), which makes sense. The thing is, I can't get it to boot at that speed for the life of me. I've cranked memory voltage, FSB termination, MCH, etc. and backed off timings to 5-5-5-15, and it'll either boot to Memtest and crash it immediately or not boot at all. That shouldn't be happening. I started getting a clue to what was going on when I made it into Memtest once or twice and saw that it detected the RAM as running at 480MHz (960MHz DDR). So it seems like that divider is messing up or something, which I suppose would explain my inability to boot.

Has anyone had this problem? I'm pretty sure I'm running the latest BIOS (0606), so I'm not quite sure what to do.

Tried it at the 800MHz divider at 5-5-5-15 (which some people say this memory can do, I guess) and still nothing. Can't even boot at that speed. I lowered my FSB to try some different dividers, all around 720MHz-740MHz, and couldn't get any of those to work either.