To say this right upfront I am still very, very new to iclone and all that relates to it.  I'm learning as I am going and I'd love for someone to reply to this and point out that I'm doing this wrong and there is in fact a good and reasonably fast way to use iRay.  Anyway, got the iRay plug in, thinking it was going to be a good thing and I'm still puzzled about what I got there.  I'm posting pictures bellow that I think speaks for themselves.  Compare the look between iClone and iRay.  There is no way to set up the lighting using iRay preview because it just updates too slow, even on a really low preview setting.  The lights look and behave completely different between the two renders.  It's not just the color.  Note the missing shadow cut in the background, the red hot spot, the missing glow of the lights, the higher contrast, the missing highlight on the helmet, etc.  I just want to stress one more time this is the same frame you are seeing!  There is no lighting change in any of them.  I'm using a Ttitan X Pascal card and rendering that ONE iRay frame in 4K took 30 minutes.  Rendering 195 frames in iclone, in 4K takes less than that on the same machine.  Now there are some things better in the iRay render.  There seems to be a more skin detail and the shadow between the face and the helmet look more realistic.  I'd also guess the eyes have a bit more detail, but from what I can see that's it.  Everything else rendered worse.  Now if there was a way to render the face alone with iRay and everything else as an Alpha, I could use the render time and composite the higher detail face on to the iclone render, but I don't think that's an option.  The iRay render options seem very limited.
Also while I'm at it does anyone know if an iClone image sequence can be rendered it more than 8-bit?
For comparison I'm also posting an iclone render that's been color graded in DaVinci Resolve.