My 2012 is newer than you are considering, but I will say with confidence that my 03 5.9 with a SmartyJR on level 2 had more power than my current truck. It would tow the same load 5-10 MPH faster up the passes than my current truck. Without the Smarty, it was about equal in speed (granted, a much lighter truck).
The 3rd generation 5.9's have a very high resale value, so you might find that you will get more truck for your money with an early model 6.7.
For your stated uses, I don't think you can go wrong with either. If you can increase your budget enough to get into a 2010, with the new body style, that is the route I would go. A true Crew Cab is a big advantage over the quad cab, unless there are only two of you in the truck.