%CPU UTILIZATION IS A LIE

Summary from the TLDR newsletter

Viewing CPU utilization is easy - just pull up a system monitor tool. However, trying to project these numbers is a bit more difficult - whenever people try, they find that CPU utilization doesn't increase quite linearly. This happens because of hyperthreading (the cores on the machine are sharing resources with other cores) and Turbo, a dynamic processor frequency adjustment technology used to increase performance. Reported utilizations are usually an underestimate, sometimes significantly so.