Markfw900 is running an Athlon64 3000+ at 2.2GHz and reports 2h 10m on the "standard" benchmark 0.417 WU used by Ars Technica. If anyone wants to do a test with that WU, I put up my SETIBench.zip kit
here and you just need to unzip it, throw in a 3.08 client (assuming Windows), and run the
RunSETI.bat batchfile, enter your crunching email, and let it run 'til it disappears. Then check the CPU time in Result.SAH.
My AthlonXP 1800+ at stock clock does that in about 3:40 on an nForce2 board, but that's so far from the cutting edge that I doubt it helps you
edit: in terms of volume production, it looks like the Pentium4C's with hyperthreading enabled are still leading the pack in single-processor situations.