Less pixel & texture fillrate with an undervolt + overclock?

1st slide stock

2nd slide undervolt @ 2992MHz + 950mV (stable) and +2000MHz memory clock.

This isn’t a problem, since my undervolt performs quite a bit better than the stock settings, so nothing isn’t working as it should, I’m just curious to be honest, because I noticed less fillrate when I had my undervolt on, does it just need less because I’m using less power? I’m curious if anyone knows the reason. Again, it doesn’t impact performance, my undervolt + overclock does improve performance by quite a margin, I’m not looking for help, or fixes, I’m just curious.