If you're already thinking of modding the Ecoboost, then that should tell you right there it's not going to be enough car for you. The truth is, you'll never pull the power levels out of an Ecoboost that you will out of the 5.0L, nor will you do it for a comparable price.
If playing around in the corners is most important to you, then go with the Ecoboost. If you're looking for more grunt in s straight line, go with the 5.0L
If you're happy with the handling of the 5.0L, then it should be a no brainer.
In any case, I can't believe you'd think the Ecoboost feels faster than your supercharged Fox body. They're only a high-13-second car on a good day. I can't believe your Fox isn't quicker than that?