This is an interesting topic,
I’ve got a older 3.0ghz 8 core i7 with 8GB of ram and I am averaging about 2.1 sec for equihash, but I am running Ubuntu in a VM so its probably not the fastest it could be. I also have an old Motorola RAZR that I plan on rooting with linux just to see how the 1.2ghz dual ARM processer with 1GB of Ram does.
With the way equihash works it directly ties Cores to RAM so the many cuda Cores on a GPU board will be bottlenecked by its amount of RAM. St4rd has mentioned he is working on this correlation before: Equihash currently implemented? - #11 by Shawn
So I think anyone building a rig will be better off focusing on CPU and RAM rather than tons of GPU.