Arnold vs Mental Ray - Maya 2017 FumeFX

With Mental Ray no longer free in 2017, I’m evaluating Arnold with FumeFX and finding the results a bit disappointing. Are there any render experts out there who’ve successfully switched to Arnold in 2017?

The main thing I’m noticing is that multiple-scattering does not appear to work for me despite trying a range of settings. Perhaps I am missing something, however. Below is an example of Mental Ray in 2015 vs Arnold in 2017.

Furthermore I’m noticing a great deal more noise with Arnold. I can adjust the overall camera AA and volume indirect samples but the noise never seems to really go away, it just gets minimized somewhat. Heres MR in 2015 and AR in 2017 below again.