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iMac 5K (Late 2015) vs Mac Pro: PhotoZoom Pro
The two machines tested here are the fastest possible CPUs as of late 2015.
This test uses all CPU cores as well as the GPU. As well PhotoZoom Pro has a special tuning feature to test GPU performance in advance.
During this test, the iMac ran its fan quite loudly; the Mac Pro remained all but inaudible.
The late 2015 iMac 5K beats the Mac Pro with a solid margin!
Since the Mac Pro is a 3.3 GHz 8-core machine with dual GPUs (!) and the iMac is a 4.0 GHz 4-core machine with one GPU, this is a pathetic performance for the Mac Pro.
This test shows just how blazingly fast the iMac 5K really can be, even in a situation where the hardware specifications suggest that the Mac Pro should trounce the iMac*.
The explanation is straightforward: while PhotoZoom Pro chews up all 8 cores (16 virtual cores) on the 8-core Mac Pro, about half that CPU usage can be seen to be system time (red in the CPU graph)—synchronization and busy-waiting overhead. In other words, PZP does not scale much beyond 4 CPU cores. Disabling all but 4 CPU cores in PZP preferences proves this to be a correct diagnosis.