This paper is great:

"Our methodical investigation demonstrates the role of ISA in modern microprocessors’ performance and energy efficiency. We find that ARM, MIPS, and x86 processors are simply engineering design points optimized for different levels of performance, and there is nothing fundamentally more energy efficient in one ISA class or the other. The ISA being RISC or CISC seems irrelevant."

https://dl.acm.org/doi/10.1145/2699682 https://abdullahyildiz.github.io/files/isa_wars.pdf