If we're bringing other films into the discussion, then IMO Heat clearly needs to take a backseat to the climactic shootout in The Wild Bunch (mentioned already in the thread).
For shootout scenes, I don't think that has ever been bested. The build up as the bunch walk to the hacienda, the pregnant pause after the first shot (there's more tension in those 10 seconds than in the entire Kingdom shootout BTW), and then all hell breaking loose - perfect. Still packs a punch today. I can only imagine what it did to audiences in 1969.
Sorry to digress