Re: Do you want the knife as a throwable option?
Either option would be cool.
If it were used as a grenade, it could essentially do more damage than a conventional grenade because it requires far more precision instead of exploding in an area of effect. The 100 damage is probably appropriate.
If it were another weapon in the game, the amount of throwing knives available would increase, which I don't think is a problem. It would basically become a short-range version of the bow and should have reduced damage to match, especially considering the speed and stealth benefits. That said, it should have severe distance fall off to prevent it from being abused to "snipe" people from 200 meters away with essentially no warning.