Well i have never emptied a 60R mag before in a firefight.
But i find it good to have a lot of ammo because then you just need to fire, no need to think about ammo. Also i should add this, some ammo was in the ammo box but i had 3 40R, 2 30R and one 60R mag on me. I was really pissed losing all that and sitting with not even a full mag left (had 36/40R mag).
and i saw the other post, have had those problems as well so not the first time i saw that post.