So (work/instruction)*MIPS? Except... how is "work" quantitized? It doesn't seem as straightforward as measuring joules. Well, it might be... a fast chip might be considered a hot one.
This is where that whole course went. The Arduino and PIC chips have are RISC computers so each instruction does very little. A PIC16 series chip doesn't even have a multiply instruction, just 8-bit addition and subtraction. So on a PIC or Arudino it might take you tens-of-thousands of instructions to 64-bit floating point division which a modern desktop CPU can do in a single instruction. By that logic, a desktop running at 1MIPS might be considering 50,000 times faster than an Arduino running at 1MIPS. But not every instruction is a floating point division so that comparision wouldn't be accurate.