Rendered again, this time 1280x1024 instead of 1280x960. All 16 CPUs (600MHz R14k, 4GB shared RAM) and it took 2 minutes 36 seconds.
All CPUs are showing load (although never 100%). At the end it does not render faster..1280x960 still had the same time as with just 12 CPUs.
On the fuel with just one 600MHz R14k CPU it shows 10% progress after 10 minutes. (still rendering)
Rendered in 5.61 seconds on my (dated) Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz with 4 cores.