My 6.0 gm will pull 8500 the speed limit or better on 99%+ of the roads I have ever been on. On the interstate just set the cruise at 65-70 and steer.
The ford 6.2 and gm 6.0 will put more power to the wheels at just about every road speed than the ford v10 or the chevy 8.1 or years past.
I suspect the 6.4 hemi will do as good or better than the ford and gm engines. It should be a good setup for someone looking to tow a larger trailer that doesn't want a diesel.