I've been taking a very simple scene recently and trying to push it to the limit. By push "it," I mean the materials and render settings. All I did was be much more meticulous about the Vray materials, adding layer upon layer of detail using composite maps, and that sort of thing. I also integrated things like in-camera depth of field effects, easily applied using the physical camera. Beyond that, I pushed my render settings to a level that I previously though was ridiculous, and perhaps under a time crunch they are, but the results are awesome. The straight on view of the chair rendered for 15 hours at 2500 x 2500 pixels, and that is on a very powerful machine (48 cores)! I used Vray progressive rendering and just let it refined until the noise threshold reached .001. I also used very high subdivision settings. Here is what that ended up looking like:
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