I agree focus is a superior proficiency. It really comes in handy for head to head gunfights, esp if you're using a silencer and need those couple extra bullets!

Stinger is insanely powerful even without using Blind Eye.

The trick is to watch for the Streak call where the game announces the incoming kill streak and then watch the horizons of the map for the incoming Helicopter / Strafe Run / Reaper / Whatever...

If you do this effectively you can actually get a Stinger lock before the streak actually is on the map as it approaches and so by the time it reaches the map you've already let a missile fly either destroying it or causing it to take evasives and allowing you to ready another.

It doesn't work 100% of the time, especially if the streak is entering the map right over you in which case you'll probably fire off the missile and then get gunned down but it usually guarantees that if nothing else you get at least 1 missile off before dying and half the time you just wreck the thing without consequence.

Almost every loadout I have has a Stinger for this reason. It's an amazing way to get easy Kill Streak points for your own streak as well.