The ride is still stiff with the coils but is definitely smoother than with the leafs in my last truck (chevy 2500). Where I really notice the difference is cornering at moderate or higher speeds. The coils really hold the truck to the road better.
The 50mph thing while towing is difficult and I'm going try but I can't imagine the hazard I'd create by going down the interstate at 50. Someone mentioned just setting the cruise control and IMO that may not be a good idea. From what I've read about breaking in it's best to vary engine speed. At least that was the recommendation for the initial break-in. I don't think you have to go nuts trying to drive at every possible RPM but just doing the same thing for a long time may not be the best idea.