Sea-saw level 66
Each Turnin of HQ items will grant a reward of 4,201,740 XP and 5,408 Gil. You will make a gil profit if you can obtain the 1 items for less than 5,408 each.
|66 to 67||7,722,000||4||2|
|67 to 68||8,575,000||5||3|
|68 to 69||9,593,000||5||3|
|69 to 70||10,826,000||6||3|
You will only gain the listed XP amount if you're within the Expansion's Level Range; A level 70+ character attempting to complete a level 60-something Leve will gain almost no experience.
Most likely you will stop doing this leve after 5 levels, but depending on market prices/etc it may be benefitial to keep turning it in well past that. Also remember to Diversify. The same quest will not always be available to choose.
Use your best judgement when deciding which level to mass produce.