I strongly suspect that the vast majority of people out there with M-2300-k installs and Fox boosters, have old boosters with one of the diaphragms torn (1/2 assist). The other major problem is that people use brake pads with very low cf. The SN95 booster is used as a crutch to get the overall sensitivity into a reasonable range. But this doesn't solve the problem of the SN95 booster having too much crack sensitivity. This makes it very difficult to modulate the brakes. Once the correct pads are installed, the Fox booster works great.
Brake systems are actually one of the easiest things to analyze in the car, but you must have every piece of information about them, and you must know that all the parts are working correctly. Every time I help a customer with a brake system that has unacceptable travel and/or effort, I'm able to fix it using fairly simple calculations partly based on known good combinations. In years of doing this, not one person prefers the SN95 booster with the M-2300-k kit, when all the parts in the system are working correctly.
My car currently has an SN95 booster (from previous owner) with a Stoptech 13" kit and a Baer 12" rear kit. Overall this base brake system has about the same sensitivity as an M-2300-k kit. The brakes suck. They are far too sensitive. When I go from the WRX to the Mustang, I lock the tires several times in the first 5 minutes of driving trying to adjust.
Earlier this year we built a Fox Mustang for Matt Farrah (Smoking Tire). The car had an SN95 booster in it when he bought it. He wanted to leave it there to save some money. We installed an M-2300-k kit that he supplied. He loves everything about the car except the overly sensitive brakes. He drives a lot of performance cars every week.
In this particular case, the posters brake system has 33.5% more front caliper area than an M-2300-k system and 8% more brake torque from the different front rotor diameter alone. Combined this gives the brakes 44% more brake pedal sensitivity than an M-2300-k system. It probably only takes 40lbs of pedal force to lock all four tires with an M-2300-k booster on this car. Not even a Cadillac owner is going to like that level of assist