I have a machine that fails the Rift's specs check because I'm running a Xeon E5-2620 CPU. I don't have any problems running the games and from what I can tell from the benchmarks I see online it is on par if not slighting better then the Intel Core i5 4590 in single threaded performance. And it has 12 logical processors, which I believe is more then the i5.
My assumption is that the Xeon processors aren't considered when performing the specs check. In any event I would like to get rid of the constant reporting of the specs issue if I could.