I would actually suggest against Glass Jaw as it lowers one of your most important heath stats significantly. Maybe consider near sighted, insomniac, or wool allergy first?[/quote]
Prefer the -X% to head health. Reasoning : Helmets negate this almost entirely and by the time that you need to have one to negate the kind of damage that will save your life you’ll have it. Before you need one if something can murder you by smashing your head, you’re going to be murdered by it smashing your torso/legs/arms/whatever (ie: The threat was too great for you, you should have just run away).
The one exception to this rule is when you have power armour but no power armour helm. Then you’ll occasionally be (unluckily) shot in the head through your army helmet/ballistic mask/whatever combo. Even then I’m fairly confident that having the extra 20% health wouldn’t have helped.
Maybe checkout the makeshift knife instead of the stone one. It takes a lot less time to craft :)[/quote]
I agree: the time to make the stone knife is punishing, however, a makeshift knife requires a spike, and I usually (remember that this is while I’m naked and not taking chances – so one less door opened is one less chance of encountering death) only get enough steel chunks/scrap metal for one of those. Stone knife only requires a stone. I’ll usually use the spike to craft my knife spear instead, as it will be my primary means of defence for the next few days. 
Early on (before I can steamroll Fast Zombie hulks barehanded), my head and torso tend to take similar amount of damage from combat.
Good helmets are hard to find compared to good 0 encumbrance armor for all bodyparts except eyes, mouth and hands.[/quote]
I tend to go full melee, raise the heck out of my dodge / unarmed skills on normal zombies, use a weapon that can quick strike and stay away from anything that can “Smash” me until I’m around 4ish or more in both. I can’t say that I’ve noticed my head taking a lot of damage – at least, not significantly vs the other parts of my body. However, I’ve never played with the fast zombie mod. Sounds like fun though, possibly next game.