Well first of all, the Surya's Staff is Cure Potency, not MDMG ^^; I don't know who casts enough banishes to find that staff worthwhile but it's certainly not me! I mean doing that trial would take 10 times more banish casts than I've ever even done in the first place.
For the Darkness MDMG staff I went RDM/SCH and meleed EP mobs down to 8% or under then went for the drain killshot. For the last killshot trial on that staff I had to kill a full 50 extra mobs because Drains would not do enough to count! I hear other people have suggested coming on BLM/WHM to Abyssea and using Cataclysm, but I preferred the low risk path.
There are two kinds of people in FFXI, those doing the laughing and those who don't know what's funny.