How fast does an admin script have to be?
My opinion has always been that if its significantly faster than me doing the same task by hand then that’s more than fast enough.
Is my time better spent developing new functionality compared to shaving a few % off the execution time of my scripts? If the script is long running its either because I’m hitting a lot of data or I’m hitting a lot of machines. In both cases the script itself probably isn’t the bottle neck and if its that long an operation I can always run it over night. A mass mailbox migration may run over a long weekend!
Speed is relative and as long the script delivers its results in an acceptable time frame the absolute time doesn’t really matter.