I always used to have an offhand 10mm smg (in semi single shots mode) I'd use to dispose of the weak opponents and a primary good weapon to deal with the dangerous ones, save the better ammo. Upshot being, if the dangerous opponents get too close, the smg in burst mode can save the day.
Pretty much what I do as well. I love the 30 round mag for the SMG, I almost never have to waste AP reloading. I usually like a long range weapon in the other slot, usually the hunting rifle.
I believe the game only has a few missions where you have to kill a bunch of things, and those are all geared at rad scorpions and bandits.
Actually both of those quests have non combat solutions, you just miss out on combat XP and loot.