Anyone know if it runs at full clock speed with 192gb installed that way?
32GB RDIMMs that work with MacPro5,1 are 4Rx4 RDIMMs, so, 1066 or 800MHz when installed to a Nehalem/Westmere Xeon.
Since the latency will be lower than at the nominal frequency, the penalty is not so much noticeable in the great scheme of things.