I've heard about 8+ GHZ Celerons (Netburst-based ones) and they were definitely on top a few years ago. I haven't kept track lately, though, and those records may have been beaten by now.
Re:The Itanic Has Sunk
by selectodude on Friday July 30, 2021 @11:51AM
(#28009282)
https://valid.x86.fr/records.html
I think that's still pretty much the bible for frequency records.
I doubt that even a 8GHz P4 would be able to beat a lower clocked more modern design even on single threaded integer workloads. The P4 had a lot of glass jaws (the non-constant shifter, load replays on misses, very narrow decoder when running out of trace cache).