Hey look! It's my mobo, my CPU's little brother, the whole nine! Nice system build, good choices.
Memtest86 and Memtest86+ are being increasingly unreliable across my last couple of systems. I wouldn't sweat it too much on it's own. Also, if it's running clean at email@example.comV, I personally would put it there and leave it there. You're looking at a performance loss of very much under 1%, and energy savings of far more than 1%. I know it's far less exciting, but it'll probably pay for itself in no time.
FWIW I'm running 4*1GB on the same mobo, and Memtest86 gives me all sorts of excuses. Right now both memtest86 and mt86+ claim to be unable to run since 'the binary cannot fit in memory' (super-lolz). I take out either of my pairs of 1GB sticks and it'll run clean for however long I want to leave it. With all 4GB previously, it would run but refuse to test >2.7GB. Since I can do 48+ hours of Prime95 on either small FFTs (CPU stress) or large FFTs (memory stress), I'm pretty sure my ram is doing great, it's just memtest86 hitting the limits of it's original humble code design.
If memtest86 gives you a hard time, but the system boots and runs clean, fire up Prime95, let it eat tons of ram and then beat on it. I've not yet had a machine that could do that reliably for 24+ hours without being perfectly stable otherwise as well. It's a good beating.
Please don't edit my signature for me. Thanks.