Interesting we have different reports. My experience was far more in line with parent's in that enabling ECO mode had <5% multicore performance drop (single core unchanged). ECO mode also lowered temps several degrees. Seemed like a no brainer for my use case.
In fact, chips have gotten so fast these days, I am seriously considering running my desktop on a laptop-class CPU. Should be able to run it near silently on air cooling alone with low power consumption.
I've been doing that with a Minisforum bd790i -- a Ryzen 7945HX which is a monster of a CPU (16 zen4 cores, with very high single threaded and multi threaded benchmarks[1]) with a paltry TDP. Minisforum even coined the term "Mobile on Desktop (MoDT)". It's a great platform that is utterly cheap for what you get (mobo w/ PCIe gen5 + CPU + heatsink for less than the price of an individual comparable CPU). Note: This CPU is usually in a laptop with a relatively underpowered cooling solution compared to the linked motherboard with a proper heatsink+fan. Hence the benchmarks have a very wide spread due to varying (usually laptop-based) cooling.
Pertinent to the conversation though, the BIOS is very much lacking, and supposedly software-based fan control is not implemented. That said, running the fans constantly at ~silent levels of rotation keeps the temps cool (you can even run the heatsink without a fan if you want).
In fact, chips have gotten so fast these days, I am seriously considering running my desktop on a laptop-class CPU. Should be able to run it near silently on air cooling alone with low power consumption.