www.basketball-reference.com has a stat called "Game Score" which generally indicates how much production a player has had in a particular game. You include all of the player's statistics for the game, and they are then converted into one stat -- Game Score.
A decent player having an OK game should have a Game Score of 10.
15 is a pretty good night.
20 is very good
25 and above is excellent
Anything above 30 is noteworthy. You can get game Scores way up in the 40s, 50s and even 60+ (3 guys - Jordan, Kobe, Karl Malone).
OK, so to evaluate what level of play is necessary for a LeBron James-led team to win a Finals game, I used the site's sorting mechanism and came up with some amazing information:
Game Score under 10 -- LeBron 0-3 in the Finals
Game Score 10-20 -- LeBron 2-10 (.167 winning percentage)
Game Score 20-22.4 -- LeBron 2 and 8 (.200 winning percentage).
Let's stop there. It makes virtually no difference whether LeBron has a 10 or a 22.4 Game Score. His team will not win those games except in the rarest of instances.
Game Score 22.5-25 -- 3-1 (.750)
Game Score 25-30 -- 6-1 (..857)
Game Score 30 and above -- 4-1 (.800)
This is really remarkable. LeBron has won 17 Finals games. 13 of those where his Game Score is over 22.5. Only 4 with his Game Score below that figure.
So - there is your cutoff. Go to basketball-reference's front page tomorrow and it will have the 5 best Game Score's posted. If LeBron is below 22.5, he almost certainly lost. Above 22.5, he almost certainly won.
According to this Site, a Game Score of 22.5 is basically 27 points, 7 rebounds, 7 assists, 1 steal, 1 block, shooting 50% and 3 turnovers. So that is your cutoff. Better - LeBron almost always wins, Worse - he almost always loses.