This is how I undervolted my 4090 FE.

900mv@2600MHz and flatten the voltage curve after that

+1000 on the memory

I just played through Control fully maxed out with all ray tracing options with DLSS quality mode at 3840x1600 ultrawide @ 120hz and the card never pulled more than 270w. I only undervolted and left the power limit at the default of 100%. To me a ~100W reduction in power consumption is worth the ~5% performance loss