[mlangsdorf]

My experience is that it doesn't change the lethality a great deal. HT 10-12 foes that are wounded to -1 HP to -1xHP usually stop bleeding on their own without dying, and foes that are below -1xHP are pretty much dead anyway. If you're using a lot of high caliber rifles, people are often dead when they're taken out of the fight, so bleeding doesn't matter much.

As Tomsdad points out, the enhanced bleeding rules from MA do increase lethality a bit more, since vitals hits (with the -4 bleed penalty and need for Surgery to stop) become near guaranteed death sentences. Without those rules, taking 5 points of damage past DR to the vitals (an arrow or low caliber bullet, say) goes from stunning and knocking unconscious to quickly killing. Skull hits are less of a problem, because there's no penalty on the bleed roll so it's quite possible for it stop naturally before you die.

My own experience is that bleeding rules rarely impede the PCs that much: they're likely the victors of the combat and have the skills, magic, or technology to quickly stop blood loss. It's the fleeing (or unconscious) members of Team Monsters that are in trouble. And again, if you're putting people into the negative HP multiples where bleeding is a big problem, your game is probably already pretty lethal.