For a long time, Photoshop ACR batched conversion was poorly engineered: it processed one file at a time (serially), so that a fast 4 core trounced a slower clock speed 6/8/12 core Mac.
But that has changed; at least in the ACR batch convert process, Photoshop uses ALL the CPU cores by keeping more than one raw conversion in progress simultaneously.
Even so, it shows just how fast the 4-core iMac 5K is, since the 8-core 3.3 GHz 2013 Mac Pro used here is the fastest Mac Apple won’t sell you with a CPU upgraded by OWC. The fast GPU in the late 2015 iMac 5K might also be factor, as well as its nearly twice-as-fast SSD (later 2013 Mac Pro builds might have a faster SSD than the March 2014 machine used here).
tConvert 160 42-megapixel Sony A7R II fileso very high quality JPEG (view settings):
2013 Mac Pro 8-core 3.3 GHz: 04:09
Late 2015 iMac 5K 4.0 GHz: 05:43 (37% longer, impressive given only 4 CPU cores)
Bottom line: a modern CPU and GPU in a Mac Pro are sorely needed, since the late 2015 iMac 5K bridges the gap by a considerable amount given only 4 CPU cores.
It appears that Photoshop ACR batch convert keeps at least 4 images in progress on 4 core machines, possibly 6 on 8 core machines. This suggests that a 12-core Mac Pro might do even better.
On an 8-core machine, 800% CPU utilization means all CPU cores are in use; values over that (up to 1600%) are virtual cores, which are all smoke and no fire, having no meaningful performance value. On a 4-core machine, it is 400% and 800% respectively.