Well, how much a QB suffers from pressure is debatable for anything short of a sack. But in my experience, people typically raise throwing, vision, and strength before working confidence. So if you can get even a hurry on him that may force a throw into coverage that results in a pick... he may not recover for the rest of the game.
You say you're out leveled... so I guess it depends on how much you're willing to risk. If you're a big underdog, and screwing up their QB is the only way to win, then I'd roll the dice. I'd run a lot of Cover 0 and bring everyone that doesn't have to play coverage on a blitz and try to get to the guy whenever possible. This is a huge risk though and if you don't get him to make a mistake early, it could turn out quite bad.
If you're not a big underdog, and have a chance at winning playing your normal strategy, I'd just go with it and hope the numbers go your way. If you have a good secondary (whether they're out leveled by the WRs or not) there's still a chance they will have take the ball when he puts it up as Bort has said that the defense gets first roll for the ball on passing plays.