I'm a long time MR user, but I'm using Corona for production since I discover it.
Actually, IMHO the MR version of your 500 is better than the corona one, I prefer MR materials results in this case. I think you have to work a little more on corona shader, than you will obtain a perfect result! And, to have a correct match, you should use exactly the same camera view and lighting, the MR one seems to be a lot worm than the Corona one. Don't misunderstand me, I like all the two version, this is just my opinion ;)
Btw, Corona has got some features that make me prefer it more than MR or Iray or Vray, using a cap of words I can say fantastic render time with no 10.000 € ws and no Tesla, with realistic lighting and realistic mood of the render, with a lot of light point and a lot of poly, that is impossible to have with MR :(
I mean, to be able to give a good preview to my client in ten minutes using a low cost WS has no price!
Have a nice render time,
Alessandro