Alright guys,
I'm back from my NYC trip. Man, what a city! Thank you for all your tips about Six Flags. Since the Manhattan taxi drivers really scared the hell out of me, I gave then NJTA a try and took the bus from Port Authority on 42nd street. It worked out very well, I arrived at 11am. KK was not yet in "normal" operation, but they were doing some test shots and I managed to get a ride. Unfortunatly we had a rollback and the ride was closed after that. So I guess I have to come back to find out how the second part of the ride feels like.
Oh I forgot: The park was almost empty, it was a weekday and I think people were waiting for KK to officially open. The only "real" line was the one for SUF: 1 1/2h, one train.