At least at lower levels (Normal/Nightmare), dual wielding fast weapons will result in significantly higher DPS. The +X-Y damage modifiers found on jewelry and rubies add a flat damage bonus regardless of swing speed, so they benefit fast weapons more than slow weapons. Things might change on higher difficulties.
In my experience, dual wielding provides higher sustained DPS, while two-handers provide bigger burst damage on your spirit spenders. Wave of Light in particular will clean out a crowd when used with a two-hander. I've switched back and forth depending on which weapons I find, and both styles felt viable.
