Last month I described my disappointment at the real-time performance I was getting in my million-digit Leyland-prime search. I have now done some testing on my wife's recently-acquired iMac, a 3.7 GHz 10-core Intel i9, slightly faster than my own two 3.6 GHz versions. Her computer was running only 4 of the million-digit search processes, because it was a replacement for a failing older 4-core iMac. Supplementing those processes by additional ones, I wanted to see how that would impact search time:
4 processes 4.2 hours 1.05 hours/process
5 processes 4.9 hours 0.98 hours/process
6 processes 5.9 hours 0.98 hours/process
7 processes 7.5 hours 1.07 hours/process
8 processes 9.7 hours 1.21 hours/process
In other words, on a 10-core iMac I can run 8 searches significantly faster simply by doing 4 at a time! Running 6 processes appears to be ideal.