The big problem with these are that I'm trying out Maxwell Render and one of the issues I find with maxwell, is that yes, your rendering looks awesome but if you want it to be crisp, you need to have a very high sampling level.
Mental ray would definitely take a lot less time to render, but you're going to do at least twice to three times the amount of work into it to get the lighting and materials done alone! (that's how I see it anyway)
I'll post more technical detail with the dual screen one...
(and it is going up today still!)