When I first encountered the problem I did test 1 stick at a time and i thought it was obvious that one stick had issues but then after I replaced that stick, i realized the other stick was also causing the error. I do think I bought all 4 sticks from the same ebay merchant so there is a possibility that he's just selling bad sticks, but their rep doesn't indicate this is likely.
I don't think I've done memtest so I will try that.