Hm...having read the previous posts, I thought I'd put in my two cents. One of my current PC:s is a human Swashbuckler, with Dex of 18. Very efficient character, can definitely hold his own in a fight, and isn't a helpless baby who needs constant protection. So really, the 20 Dex isn't necessary for the NPC to be worthwhile using in the game.Khadion is a swashbuckler. Shashbucklers are the best fighters of all thief-kits, but still not strong enough to match a real fighter, barbarian, monk or even a paladin or a ranger. His strengh (12 or 14, undecided), won't help Khadion very much in increasing damage. He won't be able to obtain high weapon profs. He won't be able to backstab for more damage.
One of the reasons why I created this mod was because I felt that the game lacks good thieves, which is unfortunate, since you need a thief to complete the game (unless you choose to install the No traps/locked doors-component of Weimers Ease-of-Use). I always had the problem of having weak thiefs, which resulted in either changing Immy to a pure thief or create a multiplayer-NPC. Khadion will fix that problem. He'll probably be the best thief in the game (not counting any other mods), and importantly, he's good-aligned. No other pure thief (counting the mods I know about) is that. But he still won't be as good as a fighter.
When creating the basic idea for Khadion, I concluded that thiefs generally are weak characters. It's probably the weakest class of all (according to me). Khadion won't be able to backstab, since he's a swashbuckler, and he's got a low strengh, compared to a fighter. He won't be able to deal damage like Korgan or Sarevok. But he'll stay alive, due to his dexterity. He'll be a swashbuckler, an acrobatic fighter-type rouge who'll be hard to hit. He won't have the heel of Achilles as all other thieves in the game have: Weak, low HP's, easy to kill for the opponents. You won't need to protect him (as I have been forced to do with other thieves), he can take care of himself. He won't kill as many enemies as your fighters or mages, but he won't make you feel "Oh, dammit, I have this lousy thief which takes one of my 5 precious slots, when I'd rather have <insert another NPC here>, but I can't since I need this worthless thief to finish the game".
And also, while I can understand the temptation to make the NPC the best and baddest there is, I have to say that seeing those stats put me off from downloading it, rather than tempt me. Now, it's your mod of course, and it's your decision to make, and I'm not saying this to be mean in any way. I won't try to convince you further than this post. It's just that I think it's a bit of a shame, for all I know this may well be a wonderful NPC that won't get downloaded because the stats hint at a 'Mary Sue'.
Anyway, good luck to you, not matter what your decision is.