We use these charts in our WFRP game which does alot of the work for you. Combined with our modified damage system means that any good hit can result in a critical result.
Last night my GM stuck me in an encounter with an Assassin, the assassin was after the head of the Ulrican church known as Ar-Ulric (for those with Warhammer knowledge we are playing in Middenland during the first Great War against chaos, bonus points for knowing how significant this guy is). The assassin tried to shoot me and take me out but I was able to hear him and dive into Ar-Ulric office and shut the door. The guy then booted it open rolled a hit on Ar-Ulric with his pistol and max damage causing Ar-Ulric to bleed messily to death. I then proceeded to fight him with nothing other than my hand axe as I had no other gear on me.
His second hit from his sword that got through my defences skewered me through the chest killing me instantly, so I fate pointed (we have a house rule that allows you to use Fate points to change any one dice role to a result of your choice) my parry so that I passed. The next hit from his dagger that passed through caused only 1 point of damage but was poisened so I died from the poison so I fate pointed the toughness check to resist. I then managed to get one shot passed his defences and rolled 1 for damage, knowing I would never get another chance I used my last fate point to change the damage to a 10 confirmed for extra damage (WFRP rule if you roll a 10) and added another 7 damage severing his arm.
All in all a tense fight, lots at stake and were it not for burning all my Fate points to survive and hurt him I would have died, now I am down 3 rerolls and should I ever be hit again I have nothing left that can save me should I die. The next session is going to be interesting.