I can attest that the 5.7 is enough. Last year I had the 5.7 and this year I have a 2013 with the 6.0 and while there is a difference, it's isnt huge. I had the exact same setup you are looking at, and for surfing its great. Even with a boat full of people it was never a problem getting up to speed or planing. The wake plate is a necessity though.
I'd recommend you try driving it with the extra weight so you can see for yourself. I'd imagine going to a 2014 with the 6.0 will be an extra $10k plus and the 6.2 would be $15k. If that's the case is go with the 2013 and 5.7.