Long story, but one has never clocked to 400 without 10% more errors than the other. They have the same cooling (lots), I've tested power supplies, switched control boards (I also got one replaced by sushi) and can't narrow it down... the only difference is the larger capacitors on the newer boards, which I noticed after breaking some off, so technically one is now broken, but is working exactly as it was before the repair. I figured the upgrade wouldn't hurt, but it hasn't helped at all.