I suppose there are probably large groups of people who care about multicore performance on the metal, but my dominant use case is herds of single core VMs, each doing one thing (well!). In this case, host CPU and memory consumption matter, and OpenBSD is very hard to beat in this metric. My OpenBSD VMs normally consume 1/4 of the CPU time and run happily in half the RAM as my FreeBSD, Linux and Windows VMs. I don't know if there is a significant performance difference on a single CPU, but I certainly don't have any complaints about performance.
