I remember the game peaking and then starting to go downhill around 3,000. So 3,000 is fine, 4,000 is bad and you are probably well on the way to that bad about 3,500. So I'd go 3,500. Alternatively, you could have no maximum gang rating but put a cap on how much per game. No more than 3,000 gang rating can be fielded in a game except for special one off scenarios.