In Tests I don't even think the limit should exist because the power rests with the umpire to stop a bowler if he is believed to be bowling in malice. Bouncers don't by definition make the batsman play, so there's little chance of six bouncers being equated with good bowling unless they're really that good; and really you can't just defend at head height, you either attack, evade or cop it. Plus, you have bowlers like Brett Lee who are good enough to bowl four balls at the batsman's chest and two at the head, so the rule is just pesky for elite fast bowlers, of which many have said a third bouncer is worth one run anyway. On top of that, plenty of batsmen can handle short balls, especially with all the pitches tending towards slow these days and the fact that many batsmen badly edge a hook and still score six for it, so it's hardly a flat out disadvantage.