average the killing team's score against the average of the defeated team's score
i like that one more.
I think this would make team games edgier. which is good
This is how I've always seen the team terminator games working. As for assassin games, I would think that having one full team be the assassin for another full team would work the best.
This is of course presuming this suggestion ever gets submitted for consideration... I have to say that I've been a bit disappointed by the turnout for this one.