Rune Blade Geomancy
Aegis Shield Time Magic
Flash Cap Mp Switch
Wizard Robe Magic Attk UP
Red Shoes Ignore Height
The formula for Geomancy is [(PA+2)/2]*MA, so gearing for magic yields twice as much damage as gearing for strength.

With all that MA obviously it makes sense to have a magic ability as a secondary. Draw Out is the usual go to OP magic attack, but Geomancers already have an insta cast 100% success attack. I think Draw Out is a more powerful skillset overall, but it is just more of the same, so I decided to try a something a little more original. With this gear setup Geomancy will do 264 damage a pop, which isn't a ton. Summon and Black Magic would probably just end up with the Geomancer as a second rate Summoner or Black Mage, so I am going with Time Magic as something to compliment Geomancy and help out the party. I threw

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After I did the last build to try and max out Geomancy, I looked back and realized it kind of blew.
Rune Blade Geomancy
Rune Blade Time Magic
Thief's Cap Damage Split
Power Garb Dual Wield
Bracer Move +1
This build will do 588 damage melee, which is good to take down most non-heavy duty enemies. Geomancy will do 218 damage, which isn't much less that the Geomancy optimized build. And it leaves the secondary ability slot completely open. Ironically I went with Time Magic again, as this build doesn't need a significant secondary ability, so might as well have something that helps the other four party members as well. I threw on Damage Split because the build has a decent amount of HP, and damage split helps shrug off small stuff.

Man, having a PSP copy of FFT sure make this easier.