I've had the same issues as you and kinda found a solution.
I play bo2 using my laptop (1366p) connected to a monitor (1080p), I play on low res and stable @75 fps.
Sometimes I'd get 1-10 fps in mob of the dead or 20 fps in farm (yeah). I've tried lot of stuff and this is what I came up with.
First open Plutonium, once you see the comand line, click on the desktop until the game is loaded, then open the game. I've had some problems like getting a no signal screen on my monitor (One solution is joining a game, just spamming the right click once the game's opened, sometimes works)
If you're still getting trash fps, change your resolution and restart the game.
It's really weird because it seems kinda random, I even though It was server's fault