Ask an Aran thread.

A quick way to let yourself know how it feels is to equip a clean Hellslayer or Zedbug and test out the speed. Personally, I'd never want anything slower than Normal, just because it's a real drag. What attracted me to Aran in the first place was the elegance in their attacks, able to move quickly from mob to mob, and using a Diesra would just feel clunky. Don't forget that you can't really recoup the losses of a Diesra later if a new, better weapon is released.