Of course Carrara should be fastest at those default settings. Look at what's going on there (or what's NOT going on if you think about it) :

Fast antialiasing
No caustics
No GI
Not using full raytracing
Low object & shadow accuracy
Low lighting quality

The biggest reason for Burrman's problem is surely caused by not using GI. Also i see several "hard" shadows aiming in different directions. It is better to use GI with one light and a few reflecting panels, than to not use GI and have 3 or 4 lights.

Burr, I would start with just one light, and also create a background gradient or use an HDRI and enable the Skylight. Set everything to lowest quality possible and see how it looks. Do all of this before creating any shaders, as the default grey material is much better to see how your light is affecting the scene. Once you start tweaking shaders, you will then be overcompensating for bad lighting. Things only get worse from there, and your render times will go through the roof. As mentioned earlier, use some reflecting panels instead of adding additional lights. This can easily replace a backlight... Also Carrara is not that slow. True, it's not Vray or Modo. But I am really shocked to hear it takes 36 minutes just for a preview? I would suspect you could find ways to shave time off your preview renders. Reduce your render size and quality settings output to the bare minimum you need to see a preview. Unless your system really is that old and this doesn't help?! :(

jonah