Earlier quoted context omitted.
Pentium 3-4 CPUS up to SSE2 from the last days of the W98SE era surely are.
I'm currently playing around with a PC I built up from random parts, based on an AMD Duron 1200. I have Windows 98 SE on it. It does feel retro. But then I compare it to my 486, and it suddenly doesn't anymore.
A Pentium II would be a better example for both: Not too old, not too recent. Yet it suits as retro and a usable machine. Enough to render some XVID videos at 360p and 420p with a good video card. Slackware, NetBSD and lot of distros would still run fine. TLS under Lynx and Gopher would still work, the same as a Gopher client.