I use a 24/28h on my single speed (which I commute on) and a 24/20h on my road bike with no issues (150lbs and don't jump curbs). No reason you cannot do that on a FG bike, but you do get more flex on the low spoke count wheels when compared to 32/36h 3x spoked wheels.

As for 36h tubulars being lighter; Does this take into consideration the extra tire you have to carry around in case of a flat? I personally would never ride a tub on the road unless I was racing or had motor support.