Magis, In all honesty, I believe the question of whether 2, 4, D will kill faster than Gly is somewhat of a loaded question. IMO, it comes down to weed specifics such as type, size and resistance to gly both natural and man made.
Here's an example: Do I believe 2,4, D will kill Pennsylvania Smartweed or Wild Buckwheat faster than Gly, in my experience it sure will.
There are many other weeds becoming resistant to Gly also, including certain types of Pigweed, Lambsquarter and others that 2,4 D will easily kill.