I am looking to install picture rail in the living and bedrooms, and want some input on the install height.

Should I keep the height a single distance from the floor, a fixed distance from the floor at one point and level throughout(this is where I am leaning, 95" from the floor at a point of my choosing and use a level and chalk line from there), or a fixed distance from the ceiling?

The house is 100+ years old so no doorway or window trim is perfectly level, and the ceiling height is not quite the same but pretty close to 9'1". I am not sure if I want to be happy with the windows and doors looking a shade off, or the picture rail not being perfectly level.