The 4.0 is kind of an ageing truck engine. Bulletproof, bombproof, nuclear holocost-proof, recessionproof, but NOT REALLY a pony car engine, IMO. The new 3.7 is a better "fit", as is the new Coyote 5.0.
It's strange, we have the 4.0L SOHC in my mom's 07 mustang, and I like the engine. It's not nearly as rough as everyone makes it out to be, and has decent grunt.