I am glad you have not had any issues with your UPR
rear suspension, however the discussion was about
front coilovers. I respectfully disagree with your spring rate recommendation. I think that high a spring rate would lead to premature wear on the stock shocks and a way to stiff ride. There is ample evidence of posts made throughout the years on several Mustang boards as well as my personal observations of front end clunking and other noises on cars using their front coilovers. Sometimes the noise is remedied by wrapping the struts in duct tape, other times it was not solved.
Not trying to bash anyone, just reporting what I think is factual and helpful for others.