DJ ..Evans says right on their site that water is the best coolant for heat transfer. I haven't heard the term rolling boil since boiler skewl.
PG doesn't work well in all systems. In my jeep engines, for example, to aid in quick warm up (my 4.0 is at operating temp within a 1/4 mile with a 70+F start up temp) are substantially bypassed. The cooling system, although adaquate, is an "also ran".