I already have several users with doing CPU rendering with E-Cycles because of the high quality and easy to use AI denoising, the extra features, the streamlined UI, support, etc.
For the out-of-the-box speed-up Currently, the best I got for CPU was around 20%, so CUDA and OptiX are still the main focus for now.
So it’s possible to speed-up rendering for CPU with E-Cycles, but it requires some clicks.