1 or 2 CPUs?

catorarn

A customer has TS running on 1 sparcv9 450Mhz. This is not recommended, but the customer is happy. However they would like to know if they will have better performance if they swap the one sparcv9 450Mhz with 2 sparcv9 296MHz.

Is there any technical doc or best practice on these kinds of decisions other than the admin guide (which talks of 2 x CPU 400MHz at least)?