For sure the Fox compared to the 02 GT. The reason I say this is the Fox is by far cheaper to mod than modular. Pick the right Fox, add blower V3, heads, exhaust, injectors, maf, fuel pump(s), gears, ect and for about 5-6K you can make 450-500 to the wheels.
The same mods will cost a little more than that and you will be limited to 400-450 and I would say the teh correct stock 5.0 shortblock will at least match that and probably take a little more.
The 5.0 with heads/cam/intake/blower just has a better torque curve all over, IMO.
Now I love my built 4.6 2v with 20# but the Fox would be a cool ride for inexpensive.