I don't expect the efficiency cores to be slow enough to have noticeable effect on response times. Rather they'll just have smaller throughput, and other cores will pick up the rest when the server is loaded.
I'm assuming you don't shoot yourself in the foot by running strictly single-threaded workflow explicitly pinned to the efficiency cores.
We have tried it for the older generation and there is definitely a different response time. Why should it be different? Surely our workload is more computation intense than others but I'm pretty sure that you'll get a difference for other workloads too.
> running strictly single-threaded workflow explicitly pinned to the efficiency cores
Those cores are slower than e.g. the cores from the (Desktop) AMD CPU we tested at the same time (offered from Hetzner). So it is rather expensive and inefficient to use Intel (Desktop) CPUs for server-side applications as we can only use their performance cores.
I'm assuming you don't shoot yourself in the foot by running strictly single-threaded workflow explicitly pinned to the efficiency cores.