Hello Dave,
I guess this is a question to the Stata, Corp. Only they may know for
sure if any optimization was done for a particular processor.
My guess would be that, It is a rare occasion that one particular user
ran the same program (do file) on two comparable machines with
different processors. But one thing is important:
given the fact that Stata licenses can cost as much as CPUs themselves
(or more?), you would probably want to maximize performance of each
CPU/core first, and then increase the number of CPUs/cores.
E.g. a hypothetic dual-core CPU at 1.5GHz may be as fast as a
hypothetic single-core CPU with 3.0GHz clockspeed, but you will need
twice many licenses for a dual core one! There are all incentives
there for overclocking, rather than adding CPUs on board.