AGGEMAM said:
Or for Vorpal let the crit multiplier be squared (x2 = x4, x3 = x6, etc) and a succesful crit is considered a CDG.
I think you mean doubled. If it were squared, it would be x3 = x9. Using the doubling would also mean that scythes do x8 damage. I preferred to trim it back a little, and help the low end a bit more. Doubling gives you a spread of x4,x6,x8. +3 gives you x5,x6,x7. It's a matter of taste I guess.
As for a successful hit being considered a CDG, you might as well make it the old vorpal. With a sword doing x4 (or x5 using my version), the chances of them being able to make the CDG save are so low as to be impossible. Consider. A +2 Vorpal Scimitar, doing x4 damage (using your version), with a 16 STR, would be doing 4d6+20. That's an average of 34 points of damage. Even dragons have problems making fortitude saves vs. a DC44 to resist the CDG.
Using the same scimitar, using my version, it would do 5d6+25. That's a ton of damage for one hit from a weapon. And that's only making the weapon a +2, and giving a 16 STR. Put it in the hands of a competant high level fighter, with 24 STR and weapon spec, you're talking more on the order of 5d6+55. If they power attack, then it just gets horrifying. It still has a decent chance of killing an opponent in one blow, but it also means that powerful villains and BFMs won't drop in one lucky hit.
BTW, replace rapier w/ scimitar in my earlier post. Rapiers are piercing, not slashing weapons. Oops.