[berkut]

I think the objective is rendering a ridiculous amount of stuff - the fact they talk about "lots and lots of RAM" indicates there's no way a GPU is going to be able to render it efficiently without an aggressive culling step: GDDR5 might be very fast, but you've got to get the data onto the GPU first and probably page data as well. This is very often a significant bottleneck for GPUs, and is another reason GPUs aren't used for VFX rendering (at high-end), as 16 GB isn't anywhere near enough.

Production-quality render implies decent lighting and materials - this stuff has neither, so shading is likely to be negligible, and then you're going to be generally constrained by ray / primitive intersection performance.

No, cheaper (for CPU) : two ~$950 CPU cores vs $3,300 GPU. Granted you need a dual-socket system and twice the RAM to balance and it's easier to stick multiple GPUs in a system than make the jump to 4 sockets, but GPUs aren't really that much of a win... Thermal output and power usage is often worse for GPUs as well.