[thejeff]

It appears that the common assumption, held at least at one point by KO, that you can only boost with one gem is wrong.

My current working theory, that is by no means fully tested or confirmed, is that 1 gem can be used to boost your level to be able cast a spell, others, up to the total of your path level, can reduce fatigue. I think I've seem mages use more gems than their level, but I haven't been able to duplicate it.