Built to Last level 70
Each Turnin of HQ items will grant a reward of 1,503,760 XP and 3,200 Gil. You will make a gil profit if you can obtain the 1 items for less than 3,200 each.
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.