[Cainehill]

IMO you want Fire-4 for site searching, first and foremost - fire gems do a lot to fix CW's gold income or lack thereof. Then you can get some summonings you otherwise couldn't easily get, possibly a couple forgings, and you have the option to act as an artillery platform, since with Phoenix power and 3 non-artifact boosters you hit F8. That's some serious firepower you wind up having available for the endgame.

And, of course - every point in Fire magic makes the fire shield more powerful, aiding in the early expansion.