I prefer the 5.7l with MDS because it will get 25-26 MPG on the highway, and the VCT helps torque. The best I could ever get with a 6.1 auto was 22. The other thing I don't like about the 6.1 is the perceived lack of torque. The 6.1 pulls harder at 80 than at 40....so it's in the programming. Easy fix with a programmer but stock it just feels weak.
I would hold on a few months and wait for the 6.4, it's reported to have 470 hp & 470 lb/ft....stock!!

Good luck