I would say it should factor in both disk and cpu.
But probably more focus on disk - factoring
in rotational speed and number of physical drives (to the extent that can
be determined). Having a quad or dual-quad core system doesn't mean that
the customer may have adequate disk to go along with that in running multiple
compact operations. And along those lines, the server may have a nice disk
backend but not have enough CPU threads available. So the customer should
really be concerned with both aspects, among others...