Mac Pro 6,1 can work with max 128GB DDR3 ECC memories. We sold lots of those memories. We do extensive testing before we ship each set. It's not practical to test every set using a real Mac Pro. Mac Pro is expensive and shouldn't be used as testing device too often. So what shall we do?
Actually, instead of testing memories on real Mac Pro, we test it on a PC board. The most compatible motherboard for such memories is Intel x79 boards. We build a PC on such motherboard and run Mac OS on it. Once Mac OS can boot, we run memory testing software to test memories. Proble solved.