personally i would lean toward less computers with keyclone software if your focus is pve.

If you are pvp oriented more pc's might be better performance-wise.

But I've only done 2boxes with 5 accounts for pve, so i don't really know if there's any huge performance difference.

Anyways, you can always try out one computer with keyclone (with 5), and if you don't like it...add more boxes.