I know the game officially doesn't support 5-6 players, but my group has 5 players, and potentially a 6th, that are interested in trying Arkham Horror LCG.
I have more than enough cards to assemble all the decks we need to play, so that's not an issue. The main thing is choosing which campaign to play that won't have issues with the player count.
From what I've heard, the scenarios will be easier due to the the higher player count, but I recall some scenarios do weird things when you're drawing 1-2 more encounter cards.
Edited by Vertrucio