If you think that is hard try to do the Rampage missions for example you have to pop yardie heads in a set time limit I think it was 2 minutes with a sniper rifle talk about having a steady aim becasue body shots on the leg and arms don't count.

Man, those sucked. I finally got 100% mission completed status (along with all the bulletproof vehicles in various garages, the destruction proof mafia limo, all hidden packages, jumps, etc), but those took me the longest. Even if you're a good shot, you've still got to be lucky that enough guys walk by in time for you to shoot them, and that you've picked a spot close enough for easy sniping, but far enough away they can't get you.

Without a doubt, the hardest missions, though there are certainly many missions harder than Bomb Da Base.