Well i just came back to it and its rock solid. 10 hours, 35 tests without error.
I guess that pretty conclusively says that the issue was all down to memory incompatibility so Ill get on ebay and stick to the memory listed on the 'tested' section of supermicro's motherboard page. I really would have liked the very low profile stuff so that its possible for me to populate all channels (one of the coolers overhangs the memory)and they don't specifically list any models of this type
Edit: thinking about it actually there are a few BIOS options that I have tweaked also. I will list my settings once Im happy that unRAID is stable.