The antigua line is far faster, but I'm not sure that it makes a huge amount of difference. For monsters that don't dodge, the valiance is easily fast enough, for monsters that do dodge, the antiqua line is not fast enough. If you want something fast enough to hit dodgers, you need a magnus line gun, but that comes with feet locking when firing/reloading and only two shots before you reload.

Personally, I switched from the (antigua line) blackhawk to the (magnus line) callahan is only fire one shot at a time to prevent the reload. My routine goes like this: "fire, shield up and try to move, as soon as I move, I fire again, repeat until the dodger is dead". When you can move with the magnus, you have waited long enough that you won't trigger a reload.

I do miss my blackhawk for whacking minerals and bushes, but honestly, that's about it and those chores aren't worth a weapon slot.

YMMV. good luck

Magnus bullets are slower.

The Antigua line is all about kiting around monsters more than any other gun. The fast bullets are offset by small bullets which require more precision with aiming. In exchange for a large clip size, the guns do less damage per bullet. The split damage is compensated with the best charge attack for guns.