I tried to drop mine to 4000 CL15 but it wouldn't manage it, only 3600 CL14, 3900 CL15, 4200 CL16.
I tested in Witcher 3 and heavily modded Minecraft ages ago and gains were minimal / insignificant at best. +200 Mhz with 2 extra cas lost a couple of FPS on average.
And Anno games also run shockingly when the FPS counter is turned on, 80 FPS in 2070 and 30 FPS in 1800 with a 10900K and 1080 Ti (they are massive CPU hogs).
I need to update my BIOS and drivers anyway so will start fresh once I get round to doing that.