Mass Combat:, The Unholy Spawn of Method's Merc Thread Options

[DocTaotsu]

So one of my big weak spots is that I love the idea of going "Black Hawk Down" on my players and throwing an entire city full of motivated Ak-97 wielding mooks at them. I desperately want to use the phrase "You have more problems than you have bullets to solve them with." (Thank you Schlock Mercenary)

But I don't know how to do this without bogging the game down into sloggfest 2070... 71... 72... 72.5... etc.

So I'm looking for some abstraction, perhaps not to the length that 2nd ed D&D went but definitely some way of resolving huge combat so:
1. Players have interesting choices to make that are shaped by their skills.
2. Given the disparity between a 400 bp+ PC's and mook NPC's... how do you decide how many of them die or are maimed so badly they won't be an issue anymore? I'm thinking of the 12+ Body troll with the gyromounted MMG with APDS laying into a wall of angry people.
3. Damage? Should we just assume they're constantly resisting some amount of damage unless they have complete cover? Kind of like a large group of full auto mooks get a persistent "suppressing fire" that operates independently of their actual rate of fire.
4. Mook Morale? Should I just make a group composure test?

Or am I abstracting this in all the wrong ways? There's some simple game mechanic I can use to resolve all of this?

Right now it's all GM handwaving.
"You are confronted by many many metas with an equal amount of many weapons. You should start running or chucking grenades... or both."
"Okay, you're shooting grenades, you're laying down suppressing fire, and you're using all your drone mounted LMG's to 'Cut them down where they stand' Uh... about half of them die and they rest run away."

It works but I'm hoping to give my players something beyond "We shoot the fuck out of them" and me saying "Yes you do! Here's so karma for all your hard work."