I traded up from a 1500 to a 2500, and from the 5.7 to the 6.4 ... kept the same trailer. I don't feel any extra "power" from the 6.4, it still takes a while to get up to highway speed, or going from a stop.
I'm not certain, but the 2500 a lot heavier than the 1500, and maybe I'm wrong, but I think the extra power of the 6.4 is going towards moving all that extra steel around.
I've never seen a 2500 or 3500 in these parts with the 5.7, always the 6.4 or CTD.
Get a taller rear end, unless this is a daily driver too? Loved the 3.92 in my 1500, and the 4.10 in my 2500.