Mine are usually 3/8" on ASL and RD.
I'm going down to 1/4" on my next ASL and RD. When they get that narrow I use a thicker overlay with a deeper groove across the top and reduced depth of the grooves on the sides.
the interesting note on glass bows I have done is that I really didint get a difference on the chrono between 1/2-3/8
I think you are on the money with the thoughts on getting more speed by reducing limb width and mass overall than by narrowing limb tips alone.
I did an experiment with weight added to limb tips on an ASL. The weights on each tip got to over 500 grains and the reduction in arrow speed was not very much. If I can find those results, I'll post them.
Here's some pictures of 3/8" tips on an ASL and an RD.
This is the RD
This is the ASL