I went from a 05 2.5 GT to a 13 3.6R limited. I think the GT was faster, but the R is quieter and much smoother on highway. Mileage is better with the R. I average about 24 miles per gallon in 5000 miles verse the 22 for the life of the GT. While it is nice to fill up with regular instead of premium, I find I am actually paying more at the pump because the 2013 has a bigger fuel tank.
I can give you more opinions later if you like tonight, since my phone is low on battery.