I've been doing some testings, and with 200++ str, 80++ luck, I do around 800 when I crit using a warrior.
I took away my strength bonus adding lapises and added in luck lapises, and with around 180++ str and 100++ luck, I did around 600-700 when I crit.
Probably, this means that crit damage is dependent on your normal damage, so strength (since it increases your normal damage, increases your crit damage as well), and for a warrior, it's higher than luck. Not sure for a hunter though.
So my guess is, to get the max damage, you need a good max of strenth and luck in a magic ratio