I have a 2013 F150 5.0L 4x4 Supercrew short box with 3.55 gears and tow a 5,000 lb hybrid with absolutely no issue. I have 7,700 tow capacity and 1570 lb payload. The truck cruises along fine, and has plenty of power. At 60mph you hardly even know the trailer is there.
A friend has a 2012 EB, same truck only difference is he has max tow and max payload. His trailer is a little larger and heavier and he has absolutely no issues either.
Both engines are solid.
I went with the 5.0L for the fact that rebates when we bought were far better, and I couldn't justify the extra money for the EB and the so called fuel economy is not that much better to justify the added cost.
If I was towing heavier or towed lots I would go for the ecoboost, but for our relatively light trailer and towing 7-10 times per year the 5.0L is perfect. You also get the hear the V8 come to life under heavy acceleration versus the whine of the twin turbo