well I went and test drove two 6.4l 2014's last night, one was a demo slt 6.4 with 3.73's with 7k on the odo, the other was a new 3500 with 4.10's bare bones work truck.
overall I would say there was less of difference between the trucks than I expected.
the slt obviously had the more comfortable interior and felt fine with 3.73 in the few miles I drove it. the suspension felt stiffer than my Tundra of course, but overall a nice firm riding truck...as a HD pickup should feel. The thing that scared me the most was the EVIC showed 11.5mpg avg. which means in reality it's probably about 9. of course I don't know how or where it's been driven but it was the owner of dealerships father who was using it.
the 3500 had a bit stiffer ride as expected, but nothing I would call terrible. I expected a much harsher ride given the 1 ton leaf spring stack but it wasn't all that bad...again everything is stiffer than my cushy Tundra.
I could feel the difference with the 4.10 gears but I would not call it night and day....I'm sure if I had my 7600lb trailer hooked up to both I would feel more of a difference.
overall I'm sure either would be fine, but the fuel economy really has me scared on the 6.4's. I know none of these trucks are great on fuel but going from ~15mpg avg to ~9mpg avg is a huge decrease given my DD. I have been watching the posts and tracking with fuelly.com and seems some guys are getting ~15 which would be accpetable, but I have to wonder if they are flatlanders? I'm in northern NJ so I'm not in the mountains like outwest, but not in the flats of Florida either.....much of my camping is north and west of NJ, and my daily drive is somewhat flat.
looking at all my options....5.7($34k)....6.4($36k)....and even a used 2011 6.7 ($35k)