Some of the Pentium 2s had cooling problems, didn't they? But with an overspec fan they were OK.
I went straight from an old 200MHz Pentium to an Athlon XP 1700+, so I never used a P2 or 3, or a K6.
One of my friends has a 666MHz Celeron, but after he got a DVD drive installed by PC World, the fan got jammed by a stray IDE connector. The processor was slowly melting down for 6 months, until I put an old Athlon XP 1700+ fan on it.