The Payton Manning type of pressure comes from being an elite quarterback in the NFL and playing at a level that no one else really does while still not managing to win a super bowl.
No one is accusing of Vick or Romo of playing at a level that much higher then any other quarterback in the league so I don't think the pressure is any worse on them then it is on say............Chad Pennington.
Originally I thought McNabb would have it, but no one really "expects" him to win a super bowl like we all did with Marino, Manning, etc.
I now think that no one has the pressure, however, if the Carson Palmers and Drew Brees of the world continue to play at the level they do now and still not win one, they could have it in another few years.