[microcolonel]

Apparently good Cortex-M7s get around 5 CoreMark/MHz (NXP crossover, STM32H7), so it's almost identical per MHz, and I'm willing to bet that they can get higher frequencies with less effort (if you look at the SiFive MCUs, they run at stupid frequencies compared to similar competing cores, and were generally available almost two years ago now). For further comparison, the Broadwell Xeon I'm typing this on gets about 7.2 CoreMark/MHz (running at full turbo, 4GHz, on one core).