I don't think there is a generic answer to this. A valve designed for 3/4" supply lines will generally be able to supply more than a 1/2" one. Unless you are using numerous showerheads, max volume is not the concern.
Most thermostatic valves require two knobs or levers (or a combination); one for the temperature setting, and one for volume control. Pressure balanced valves typically only have one valve and turn on with max volume.