There's plenty of times that extra compute capacity saves money, but not spending $5K to get a relatively small bump in clock on one chip. $5K will get you way more compute power if you just spend it another machine.
Just the mere fact that such a processor exists,is not in the official catalog and costs substantially more, tells me that there's adequate demand for these or at least the particular customer has very deep pockets if they can ask for custom build.
