AbdulAlhazred
Legend
When I want a "quick and deadly" variant game, I halve the monsters' hit points and double their damage dice. So a quick and deadly orc berserker (normally 66 hp, 1d12+5 damage) would instead be 33 hp, 2d12+5 damage.
I used this option a lot in my Fall of Civilization campaign, but they had 2-3 leaders in the (large) party. A couple of the most memorable encounters in the campaign were with monsters using this variant, though. I haven't playtested this is a leader-light group.
The problem I see with this variant is that it REALLY devalues anything EXCEPT damage. There's not a lot of point to careful positioning, control, even in-combat healing, when the fight is over in 2.5 rounds. Certain conditions become super strong but overall it turns into a slugging match and from what I've seen high damage output for the quick kill just blows the doors off any other kind of tactics. Seems to rather miss the whole point of 4e combat. I guess you can call that Old School, but having been there from day one my biggest complaint with older-Es was that monsters just can't stick around long enough to do much.