if we're talking about relative human-experienced performance, the slowest computers i ever owned were in the early-mid 00s. they sped up as multicore and ssd's entered the picture and plateaued about ten years ago ime.
The most striking performance observation of my experience was that Apple took a system, OpenStep 4.2 which ran okay on a 33 MHz 68040 (and acceptably on my 25MHz Cube) and made it run only a little bit better on a 400MHz G3 as the Mac OS X Public Beta.
The difference of course was anti-aliasing, and much greater bit depth, and running multiple programming environments/toolkits (Carbon and Java).
