I just did a C3 on myself for 586 HP. In town, Iceday, no Aurorastorm blabla. Capped power, capped Cure potency, Glorious Earring, 1200 JPs, Afflatus Solace. (I suck, I don't have a Queller Rod. That thing doesn't exist.)
(340 + 30 + 5 + 5 + 6) * (1 + 0.5 + 0.02) = 386 * 1.52 = 586
The absolute cap I can come up with sans Cure received potency is all that + 5/5 Kaykaus +1 + Queller Rod + Janniston Ring, which is +23% Cure potency II.
If it doesn't cap lower, that's 667 HP.
(340 + 30 + 5 + 5 + 6) * (1 + 0.5 + 0.23) = 386 * 1.73 = 667
I don't have maxed job points (I think 11/15 solace) but last time I did a Cure III without Aurorastorm it was 649. No potency received, no Janniston Ring, I honestly can't believe people actually pick that ring.
As such, those 649 might have been powered by Lightsday, or so. There is no way you can hit that without Janniston Ring, let alone Kaykaus +1 all over the place.