The only reason I'd want 6 companions is if I also get to create my own party. Right now I'm fine with four because I'm not keen on dealing with pre-made companions. While I like games like Dragon Age and Mass Effect, I don't necessarily enjoy all the companion interactions. Overly written companions control the narrative too much.. If I get to create my own party like in IWD then that's more fun for me because it's my own soap opera that I'm creating. I get to create the characters personalities and stories as I play the game. If it's someone elses characters then my brain goes all grumbly whenever they do something out of character for the character I'm trying to play them as.
