Do full length and shut up. Consider yourself lucky that you can add MM SFC! I on the other hand, choice of SFC that I can use is very limited(which I,m getting ASA my tax return gets here
Do you have a panhard rod or spherical bearing control arms? if you don't have something to locate the rear axel better you won't notice the subframes as much.
there are multiple problem areas on a mustang. rear axel location is the most overlooked problem IMO. could not belive the differenc the MM drag arms made on my car. In hindsight I would have bought the parhard rod as well.
It might be because I have a metal ass. Couldnt tell a difference when I changed my midpipe. Well other than that I lost low end power, but couldnt tell a difference up top. Then, when I installed my LTs, I couldnt tell much of a difference.
I don't agree with the 'night and day' thing either but I'm sure it helps in the long run. If yours is a daily driven car, you may not get much out of them. If you occasionally go to the track and hit it hard, they'll help keep your car straight.
At my last job I parked in a parking garage. Before installing the subframes I could feel and hear the body twisting when i turned up the ramp. Once the subframes were installed there was no more flex and the car felt much more stable when on uneven surfaces.