Personality System Data Collection [WiP]

You would gain it all.
In fact, I think you would gain all 600 even if you were at 499 before you did the quest.
At least, that's how it works with Ambition: I regularly get my ambition to 495+ (1 Zak, 2 Pap, and a few random area bosses) and then do zak or von leon, and end up with around 800 Ambition for the day. (It says 500/500 in the window, but looking at the actual Ambition value, I know I received the full amount).

i can personally confirm it works like this, i wasted the 200 and 400 ones, but ended getting almost 1100 the third day, lol