Keep the 2000s...
Those who need more than 2000 a game are a small minority. It's not a big deal to tear open a second bag to fill a 4000 round ammo tube every few weeks. Plus, 2000 round bags are good for pouches. And it would suck a lot less to tear/spill a 2000 round bag than a 4000.
....however.... I wouldn't mind seeing them in a well designed bottle with a spout.