hehe you noticed my lack of patience.... ^^
OK I took one out and didn't have a crash for a couple days (a crash-free day was rare beforehand). I chatted to someone else and he said his friend had had frequent crashes and the fix was taking the 2 sticks out of 'dual mode' (I think that's the correct term), where they are in he same coloured slots. I've tried this and I've been crash free so far and here's hoping. If I do crash again, I will continue with the process...
Have you run a memtest at all?!
Nope, but if I fix the problem do I need to?