I remember once
Doings some work on a custom telnet client for a guy selling applications into business.
He also sold hardware. Branded Apricots and generic PC clones, All DOS 2.x stuff
"Look" he said "How my DOS database application runs 5x faster on the Apricot, than on the Clone!"
"That does not compute" I said 'let me take a look"
Yep. On the Apricot config.sys was configured with 5 times and many buffers for file caching as on the clone. I adjusted the clone to the same.
"Look" I said "The clone is faster"
I never got asked back.