I honestly think he'll approach 50. The game is going to be a bit more open, the goalies pads are smaller, and most importantly teams are going to have a ton of PP's. I expect scoring to be significantly up, but I also expect that Gagne will be in the top 10 goal scorers, maybe even approach the top 5. This is the year Gagne breaks out and combines his elite defensive play with his offensive ability.
As for Carter vs. Gagne, I actually wouldn't be surprised to see Carter out scoring Gagne in 2 years. This year I highly doubt it and next year probably not, but after that Carter is going to score a lot of goals in this league.