cromda - good test. I can't explain 10x.
I am willing to believe 2x difference, maybe even 3x, for similar code on PIC32 vs STM32F, but 10x has me flummoxed. For a difference that big, I assume the algorithms are different.
I did read that the PIC32 UNO tool chain contains a proprietary part 'for performance reasons' but I have no idea what that may mean.
Maybe I need to get one of those PIC32 UNO's.