For a serious comparative, you should use the same light setup. Also, don't use any converter, but convert by hand with the better setup.
If you want to try, this is my old test, converted by me, from FStorm file to Corona 1.3 (yes, I should try with the new Corona v1.7) .
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--- LINK--- If you look the 18 minutes FStorm test (
Titan X + GTX980Ti) and my test with very old i7 970 six core, (15 minutes) Corona wins.
Why? Because with less rendering time and with very old CPU I have more or less the same quality or, even, better quality than an expensive dual GPU rendering.
Of course, we should try with the new version of Fstorm and Corona v1.7. Also the Fstorm original rendering ( I found it in the FStorm forum) was in JPG and not in PNG.
But, I'm very curious to see a test with two rig with the same price. For example, a new 1000 GPU (two GTX 1070) with new 1000 CPU (ThreadRipper 1950X) with the last version of both softwares.
PS: remember that in Corona v1.3 there weren't any bloom or glare.