You aren't going to use these features on extremely old GPUs. Most newer GPUs will have spare shader compute capacity that can be used for this purpose.

Also, all performance is based on compromise. It is often better to render at a lower resolution with all of the rendering features turned, then use upscaling & frame generation to get back to the same resolution and FPS, than it is to render natively at the intended resolution and FPS. This is often a better use of existing resources even if you don't have extra power to spare.