Master staff will add 2000 damage to the initial hit. Assuming you spam clench (probably not a great idea), that staff would add at most 2000 dps if you do nothing else but light attack. Monster sets will typically do 1k minimum and scale up from there, often sitting around 1500 dps depending on other factors. As most people would use clench as a dot and also probably be doing things other than clench and light attacks, I don't think it's a dps gain at all for the fire staff.

Lightning master staff has some potential as the morph actually turns it into an aoe spammable which has actual synergy with the master staff ability.