I really never liked the sound of most Ford motors. It was just something about the overlap of the exhaust valves around 1.5K R/m.
However I have been running the same Flowmaster SI/SO system for the last 9 years, and wouldn't want any thing else. When my OEM rusted out I replaced the complete "cat-back" with mandrel bent 3", and 2.5" dia. stainless steel pipe; along with the aforementioned Flowmaster muffler. Most of the OEM installs that I have seen have short bend 2.25" pipe from the converters outputs.
I tried the "muffler-less" hook up but couldn't stand it for any given time. In an Expedition the exhaust drone was intolerable, and no improvement in performance could be determined.
It is possible to tune the sound performance of a given installation by changing the relative positions of the components. For a given exhaust system you can change the sound parameters significantly by moving the muffler either forward or rearward of the OEM position to effect such a change. Basically the sound will be a little louder and deeper if you move the muffler rearward of the standard position. That is either behind or above the wheels (Differential) toward the bumper.
Mounting the muffler closer to the engine for a given installation will result in a "softer" sound at lower R/m's due to the capacitive reactance of the muffler with respect to the reluctance of the length of pipe following the muffler to the rear. Moving the muffler behind the differential has the opposite effect. I have had good experiences substituting the 2.25" pipe for 2.5" mandrel bent pipe which gives me a definitive improvement in both lower R/m torque and sound. Mandrel bending gives a more gentle flow path resulting in better flow.
Due to the rear window my exhaust is still placed behind my PS rear wheels.