[Cainehill]

3 non-artifact booster : the flame helmet, the fiery skull (only requires 1F and 1D) and a staff of elemental mastery. The first two are dead easy, as long as you acquire any amount of fire gem income, and your pretender can forge the last as well. (There's also Robe of the Magi and Ring of Wizardry, but those tend not to be easily obtainable by Pangaea of any flavor.) If you only have 2 of those, that raises you to 6, and Phoenix power gives 7 - that's a lot of devastation you can cast without too much fatigue.

And sure, the level 4 sites are few and far between - but they also tend to be better, and you really do want all the fire income you can get. Once again - if fire didn't tend to also be so handy on the battlefield, I might not recommend taking it to 4 - water and air, by comparison, have relatively little reason to take past 2 or 3 imo.