I looked more closely at the vimeo movie showing the GPU rendering of the Audi R8.

The rendering speed was around 1240 K samples/second, with what looked like 4 bounces (it was doing about 5000K rays/second.)

I have now the same CPU, the Intel I7 860, as was used in that video. After making a couple casual setting changes, I get 750K samples/second in CPU ONLY - NO GPU!

Looks like there is a teeny bit of smoke and mirrors in that demo. If you have a blazing fast CPU, the GPU is only a tiny incremental improvement, if at all.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)