Both the 3.5 Eco and the 5.0 V8 are good engines. Both will perform well. However, having driven both quite a bit, I certainly do not agree that the 5.0 can outrun the Eco at any speed contest, from a dead stop or 20-up or 50-70, or whatever, pick one. 90% of the Eco's torque is available at less than 1900 RPM, and its over 100 ft lb more than the 5.0 at that engine RPM. If anyone feels their "seat-of-the-pants" dyno gives the nod to the 5.0 either isn't running similar trucks (rear end ratio, weight, or those power-consuming 20 inch wheels), or doesn't know how to drive the Eco.
The 5.0 sure sounds better while doing it though, you just can't get the Eco to sound good. You can make it louder, you can maybe make it a bit quicker, but you can't make it sound like a V8.