Personally I view grittiness as less a mechanical standpoint and more a visual/Roleplaying standpoint.
I know my first campaign will be quite gritty. The combat will be fierce and violent and dirty. The world around them will be unforgiving and its creatures resourceful and cunning.
I will still keep the basic rules, but bring in things like:
-Multi-stage encounters, where players cannot rest and are flung back into the fray.
-Extended rests being disrupted by storms, enemies, sickness, etc.
-Serious injuries being Roleplayed out.
-Having fewer resources both in supplies, repairs, and knowledge of an area.
-Really making it seem that the players survive and manage to survive not from luck, but because they truly are; more resourceful, stronger, and simply have toughened it out.
So essentially it isn't the rules that make grittiness in my games, it is the world and its environment and how you play out this world.
I really don't think actual deadliness makes a setting gritty, it is the feeling that it CAN be deadly that does.
I guess my grit is more Pulp meets Noir. Then Warhammer Grit.