See the MPG computer wishlist at B&H Photo.
Focus stacking makes one image with unlimited depth of field (sharpness near to far) by merging multiple frames shot at different focusing distances. These shots of Shimano biking parts were done with focus stacking.
While four CPU cores may be plenty for many uses, photographers doing things like focus stacking can benefit hugely from 6/8/10/12 CPU cores, that is, when running programs that efficiently make use of the cores (e.g., 8 cores gets the job done in about half the time of 4).
Here, Zerene Stacker is doing a focus stacking job that takes a few minutes on an 8-core 3.3 GHz Mac Pro. It uses all 8 CPU hardware CPU cores very effectively.