I saw one modder who builds show piece systems use the 7740X or whatever it was called, but that's the only time I've ever seen one in the wild.
5Ghz really isn't that big of a deal any more. I know some programs benefit from it, as do games, but these days it seems easier to add more cores and develop your software for that, at least with the Infinity Fabric technology. We've had 8 cores since the 5960X, but they were prohibitively expensive. Now we have that level of horsepower (minus 200Mhz) for a third of the price and with room to grow. X99 only offered the 5960X and then the 6950X, which added two more cores, lowered the clock speeds, and increased the price by €600.