Shield to Shield

One allowance here buys 540,610 EXP, which places it 3rd of the 3 Lv 78 Armorer tradecraft leves that record EXP. The best of them, Trial and Error, returns 1,711,940 EXP for the same allowance, 217% more.

Across that rung the return runs from 540,610 EXP to 1,711,940 EXP per allowance — 3 distinct figures spanning 217%, so the wrong pick leaves 1,171,330 EXP of the allowance unspent.

On whether to wait: the best Lv 80 Armorer tradecraft leve returns 935,000 EXP per allowance, 45% less than the best on this rung, while the Lv 76 rung behind tops out at 750,330 EXP.

At Lv 78 this data holds 27 leves paying EXP across 2 categories: the 24 Tradecraft ones average 955,432 EXP per allowance, the 3 Fieldcraft ones 2,129,178 EXP, which puts this leve 43% below its own category's average.

Dwarven Mythril Shield ×1 is a Lv 79 Armorer recipe, 2 steps deep through 3 intermediates, costing 20 units of raw material and 41 crystals.

Handing that in returns 27,031 EXP and 87 gil for every unit of raw material the order swallows, and the tree needs Armorer, Blacksmith and Goldsmith.

The record carries a repeats value of 2. This site reads that as 2 further turn-ins on the same leve — an assumption, because the source data defines no meaning for the field — which would put the ceiling at 1,621,830 EXP and 5,241 gil for the 1 allowance it costs, or 1,621,830 EXP per allowance.