I have to ask when it comes to the 2 valve PI trucks what gains can we expect from a custom tune?

My truck will be receiving OBX LT's Troyer fans. 4.56 gears and 33 inch tires.

My question is what gains can. 2003 F-150 5.4 expect to get through custom tuning? I only ever seem to hear from the 2 valve crowd how good the custom tunes are.

I want to get some real world reviews and info from the 2 valve crowd.