Go with DR 5/- and light fortification, if you ask me.
I think I'd borrow these from the barbed devil:
Barbed Defense (Su): Any creature striking a barbed devil with handheld weapons or natural weapons takes 1d8+6 points of piercing and slashing damage from the devil’s barbs. Note that weapons with exceptional reach, such as longspears, do not endanger their users in this way.
Impale (Ex): A barbed devil deals 3d8+9 points of piercing damage to a grabbed opponent with a successful grapple check.
Not 100% sure if Impale is exactly what we want, but it's close.
Go to +12 NA, I think.
Added to Homebrews.
I used the standardized dire and fortification abilities.
I prefer the +12 NA as well. I'm not sure if we should retain impale, but we should at least note that spined defense applies to creatures grappling the boar.
CLIMATE/TERRAIN: Arctic to temperate
Armor boars often make their homes in caves or in densely overgrown wooded areas. They can be found in hills, mountains, forests, broken terrain, and occasionally on plains.
"Any cold or temperate land"?
Should they have extended reach with their long tusks?
CR 5?
Armor boars grow up to 12 feet long and 6 feet tall at the shoulder, they weigh as much as X pounds.