Use this spreadsheet I made to calculate Wildfire damage. Should be 100% accurate unless MDB/MDT is factored in, I don't know their precise truncation or floor order for that.
https://spreadsheets.google.com/ccc?...CKmuhqwP#gid=0
What the guy replied with the gearset is correct, but I just want to correct it on atma. Smoldering or Lone Wolf / Hell's Guardian / Ultimate is the best. Not by much, and second fire affinity atma is still a good alternative for people who haven't killed PW. Smoldering / Lone Wolf / Griffon's Claw is best while brewing.
Edit: saw some gear that can be improved on that
http://www.ffxiah.com/item-sets/183265 gearset
Head: Anwig Salade (AGI+4 WSDMG+2% MAB+2)
Neck: Artemis' Medal, during full moon only. Only bother if you are using spellcast.