My disc brake equipped road bike is multi-speed. I often exceed 40mph on descents where the number of gears available wouldn't matter. I also ride on flat lands where even vintage rim brakes with ancient/hardened pads are adequate, so I understand the incredulity expressed by some toward disc brakes. In order for disc brakes to perform better than rim brakes, rotor size and pad compound need to be optimized for the application. There is more friction available on pavement than dirt; don't get the wrong idea from discs intended for cyclocross bikes. For your weight and speeds I suggest a minimum 180mm front disc (bigger is better) and be sure it has plenty of mass to handle heat. Wispy spidery rotors look neat, but don't perform as well as stout hunks of metal.
The bottom line is disc brakes are good, just as you imagined.