Thank you, feedback is always appreciated.  The more I think about it, the more appealing a small group seems.  And I agree that unpredictability needs to be taken into account (contradictory as that might sound).  That's kinda my biggest concern right now: designing exercises that are open-ended enough to give players some freedom and encourage strategic thinking, but not so much so that things drag on too long or people get deadlocked.  

I've been considering adopting a point system for trials that don't end in character death, where characters who accomplish their goal or are more successful or efficient in their attempt are rewarded a higher number of points than those who fared worse.  Characters with higher point totals could be given small advantages in later trials.  It'd be another way to encourage allying with or siding against other characters, to either team up with the current leader or conspire against them.  But that idea is still on the drawing table.