If I were to generalize what I see
here, I'd say an AthlonXP with the bench1280 settings with mame 0.68 will give you the best overall performance.
Since there are no Duron samples there oyu really can't compare with a Celeron.
However, it is my opinion that anything above 1.5mhz AMD or Pentium is enough for most of what you'll ever play in mame.
Now, other emulators, that is a different story....