I just went to solo PM7-5 as 95SAM/NIN and got Tenzen down to under 8% HP and he never gave up. I've read posts on other strategy sites that says he gives up at 15%.
BTW, GM's are pretty much useless for any "in-game" help so just fire all of them since all they do is either tell you to blist someone or come to the forums to post here if you experience any problems in the game.
Oh, this is my 1st and last post because i feel that forums doesn't get the job done.