I'm assuming that if Apple approved it for sale, they did their own internal testing and gave the okay on the performance. Chances are, though, they did so on the latest and greatest desktop model.

With that said, I had some Mac-only friends who were interested in XIV, but I cannot in good conscience recommend the Mac client to them if performance is awful even on current gen hardware. (Then again, one of them works for Apple; she might have some choice words to say to SE and mayhaps could get something done better than the rest of us.)