Mainframe cost metrics – $$ per MIPS?

A consulting company has informed us that there is a generally accepted rule of thumb for determining mainframe cost efficiencies, i.e. dollars spent per “MIPS” of the processor(s). Where might this ROT be documented?

Their target is $12k/MIPS (hardware, software, ops staff, sysprog staff). Comments?? What variability in the numbers might be appropriate based on enterprise size?

If this benchmark is used, what cost components are included?
Systems software alone, or apps software, too? Is printer consumption of supplies and paper included?
In staffing, do you include DBA salaries in tech or apps?