i run a dual core intel 805d which is originally 2.66ghz. finally today i got my arse in gear and bought an stupidly large zalman 9500 heatsink, and now happily run my 805d at 3.8ghz.
according to tomshardware benchmarks, the 805d which costs around £85, clocked at 3.8ghz owns even the pentium 4 extreme editions and athlon fx57, both of which are silly money.