I do have a ticket open with Gigabyte who linked me to a newer beta BIOS than is available on the website for the D3HP which they thought may address the issue. Unfortunately I got a BSOD within 40 minutes of applying this and sticking all 4 sticks back in (did 10 minutes of browsing and left it at idle and it died on its own). So obviously they're working on the issue but haven't cracked it yet. The BIOS seems otherwise OK so i've left it be, but got shot of half the RAM again.
Oh and I didn't have a single crash in 3 days of running the F4 BIOS (the current proper release for this board) with only 2 sticks in
I'm in a slightly awkward situation now as the cooler that was bundled with this board has a couple of slightly bent fins because i've had to take the fan off it about a dozen times whilst mucking about with the RAM (its oversized stuff so you can't get it out of the DIMM slot nearest the CPU any other way). So it would represent a problem taking that back if the board needs to go back.
Is any other board manufacturer having similar issues by the way or is it solely a Gigabyte thing?