OK. Here is my experience with no bias to anyone. I am not beholden to any company BMR, Fays, J&M, etc, etc.
I have had many s197 Mustangs (4).
I have lowered 2 with P springs.
I have used 3 different relocation brackets
Adjustable panhard bars,
Koni adjustables, Tokico adjustables,
Steeda, Saleen, SR Anti sway bars.
Many different wheel/tire combinations.
My experience, as would be expected, is that a lowered car handles better. Lower center of gravity, etc. It must.
Lowered cars have a poorer ride from the standpoint that there is less spring travel. Whether progressive rate or constant rate, there is less allowable movement and therefore poorer ride quality the rest of the suspension being equal.
The watts on a stock ride height Mustang is better, IMO, than ANY lowered car that uses a panhard bar. You cannot change the fact that the PB pushes the axle sideways. The watts does not. The watts gives the car "tied down" feeling and moves through curves, especially if bumpy, i.e. potholes much better than the PB. Though lowered, the PB does not move as much and as such you could say it matters less as there is less possible movement of the body up/down and therefore less movement of the axle side to side.
I've had both Fays2 and BMR. The BMR has made no noise other than the exhaust pipe which will make contact with the watts unless adjusted JUST right. The Fays2 was the same exhaust wise, but the constant squeaking no matter how many weeks you spend under the car is simply not acceptable.
The Fays adjustment is a miserable, finicky deal and not worth another week of anyone's life unless they are absolutely a masochist.
Yes, my car now looks like a 4x4 which is not as eye pleasing to must folks. The ride is MUCH better. Ford did the setup because people want both comfort and handling. I would put my car up against any lowered S197 any day. The combination of Tokicos, bars and watts are just great!
I am also done with summer uhp only tires. I don't have 80+ degrees for the tires to work properly very often. Plus bumpier and transmit noise to the cabin.
All just my 2 cents.