Colder temps for coolant will produce more power in performance applications, stock engines I think it's insignificant. That's why race cars ice down their intakes etc, to get the whole engine cooler, not just the incoming air. For street vehicles it matters what capacity of cooling there is. If a vehicle can't easily maintain temps with a stock thermostat, then the issue is everything but the T'stat. The Fox Mustangs are well known to not cool well, mainly due to the lack of openings for the radiator. The grille area is tiny, very very small, so changing radiators and T'stats doesn't have that much affect.
I mistakenly(I think) have a 160 T'stat in my 98 Explorer right now. I thought I installed a 180* unit, but the temps suggest I'm way below that. I have just enough heat for Winter, but I'd prefer another 20* of coolant temps.
With a proper electric fan(reliable controller), you can adjust the coolant temps easily, above the thermostat rating. If everything is right, you should be able to install a 160* unit, and set the fans to come on at anything you prefer, 180*, cooler in Summer, warmer in Winter etc. It just needs to be high enough for the PCM's expected sensor inputs, so it stays in closed loop, and doesn't throw a code.
92 Mark VII LSC SE - soon OBDII and 4R70, GTC kit and 347, custom paint.
98 Explorer Limited project to add 4WD, XP8 parts, KB blower, paint, 337.
99 Limited mail vehicle, SOHC 4WD, later 306/4R70W swap. 1998 Mountaineer spare. 72 Ranchero 351 Clevor project.