Players Guide
Nice guide, lots of good stuff in there.
I may be reading the WFRP book wrong, but looking at FATIGUE & STRESS starting on page 62 it makes pretty plain that any mental characteristic can be distressed and any physical characteristic can be fatigued. Toughness and Willpower are used for unconscious but you could be strained by gaining 3 stress overcoming your 2 FEL and 3 fatigue overcoming your 2 AGI.
Yes, you are correct and THANKS for the comments.
I hadn't made it clear that it is my house rule that Toughness and Willpower are the standards (for simplicity). I'll add that note.
jh
I like the rule as it stands. It gives players a penalty for having a "dump stat". 
I thought about house ruling "whatever is lowest is used." Dump stats seem less pronounced now as in other systems/editions.
Typically as a GM, I constantly barrage my players with dump stat skill checks anyways, so they know better but there's always some dummy player who min-maxes a Troll Slayer..."Ohh, goodie. You made a character who's min-maxed and has no personality. HOW ORIGINAL." I detest troll slayer and pit fighter characters. They are the epitome of empty, mindless wastes of paper. I love killing them off (as I've already done once in 3E).
jh
BTW, I did up the Halfling over in the House Rules section.
jh