Comment The machines may need to be heterogeneous (Score 1) 150
You may need a (screamin) front-end machine that splits up the work and hands it off to multiple multi-core machines. These multi-core machines may only be available at lower clock-speeds.
Dont just "look at your application". But look at what parts of your application are subject to parallelism and what parts must stay single threaded. You may need a special single-thread machine that can keep the other ones fed.