> you definitely feel a considerable amount of extra latency everywhere vs. e.g. a 500Mhz PowerBook G3 running OS 9 or OS X 10.2-10.4
Odd thing...
While I agree regarding the snappiness of older OSes, the Mac was for me always a bit of an odd exception.
I started on Macs in the 680x0 era and Mac System 6, and I worked on them through 7.x, 8.x, 9.x and into OS X.
For me, no PowerPC edition of either Classic or OS X ever felt as responsive as Classic on a 680x0 Mac. I narrowly missed out on a Quadra 840 on Freecycle over 15 years ago and still regret it -- that was the fastest 68040 Mac ever made.
NeXTstep was of course originally built on and shipped on 68030 -- it's a CISC native OS. PowerPC Classic was always mostly running emulated 680x0 code.
I read analyses of Mach API calls that explained that calls on RISC were less efficient in register usage or something.
But then, Intel Macs came along. Mac OS X returned to x86 from PowerPC. And suddenly Mac OS X felt snappy again in a way it never did for me on PowerPC.
As an old-time Motorola user I was conflicted about Intel Macs. Macs weren't meant to be PCs. I didn't want Windows on a Mac. But the feeling of using 10.4 on Intel converted me: it felt snappy and responsive in a way Windows NT never did on Intel.
(NT was built on RISC and ported to Intel, the reverse of NeXTstep.)