As you well know it is not just hte weight but the wind drag as well.
I guess it all depends on how many miles a year you tow, what distance each tow is, and at what speed.
If you want to get out on the interstate and run 70 mph then I would stick w/ a diesel.
Local and short trips - I would go w/ the ecoboost. It will amaze you at the power.

I tow 6500 lbs large boat that blocks a lot of wind. I can tow it anywhere at 70+ mph no problems. It really is amazing to me how good it does.