Yes, but there are no before/after examples. I have specifically made a scene, originally for Corona renderer, to test these kinds of scenarios. You can find it here: Cycles Performance
It will require a HDRI map, which I can not redistribute, however you can get it directly from here: http://illuminatedtools.com/Downloads/ext_LateAfternoon_Mountains_CSP.zip Just plug it in as an environment map and do not change rotation, and you should get an identical result. The scene itself is set up without any ambient fakes.
If you decide to test it, just please post a proper comparison. Meaning 2 images (regular Cycles vs E-Cycles) rendered with the exact same settings, exact same time limit, and both without denoisers. (We are comparing sampling performance here, not denoisers).
Best way to compare noise levels is to see two images rendered for the exact same amount of time on the exact same machine with the exact same settings. Anything else is just biasing the results.