Boris’ work is a total overhaul of the 172’s sounds. FSRealistic adds some small sounds for things like ground roll, engine start, etc, but not “big” sounds like the engine. I love FSRealistic but disable mostly everything with the C172, since Boris’ is much more comprehensive and totally custom to the aircraft. I leave FSRealistic sounds just for the things that Boris doesn’t have, like random noises, ground effects, wind, cabin ambience, and whatnot.