My cooler covers the first two RAM slots, and the front fan on it more than covers the second two, but I decided to try a bit harder and have been able to test individual sticks. Here's the results:
Configuration - Time(h) - Passes - Errors
Stick 1 Slot 1 - - 4:30 - - - - 9 - - - 24
Stick 2 Slot 1 - - 1:53 - - - - 4 - - - 0
It appears we have a winner! However, the first time I booted into Windows with the one good stick, I got a Hyper Transport sync flood error. I've had these before, but assumed they were to do with whatever else was broken. A quick Google doesn't yield any particularly satisfying results. It appears to mostly be motherboard related, and can be fixed with a BIOS update. Sometimes.
I'll keep looking into this HT sync flood error, and perhaps put the one good stick through an overnight test. Are my above results good enough to send a grumpy letter to Ebuyer on? The RAM clearly isn't doing too well, but the other error makes me wonder if more is broken too. Thanks again for all your help guys.
Niko =)