All very well, but when the French army ran short of grain-fuelled prime movers in Spain, weight became an issue.
In point of fact, weight of the weapon and the means to pull it are more relevant than the weapon's capabilities.
Adkins, WATERLOO, has some very interesting things to say about shortage of draft animals in the Fr army in 1815 and about the awkwardness of the standard ammunition caisson and the difficulties in moving it about with only 4 horses. And from what I can see, the French were using the new, super-dandy Systeme An XI 6-pdrs, not the Gribeauval 8-pdrs.
Of course, we must remember that at the same time the Fr chose the Systeme An XI 6-pdr as their weapon of choice, the RA and RHA were upgrading to 9-pdrs.
In any case, the burining question of the hour is: "How many different types of wheels were there in the GS?"