The thing is, a gunslinger (to me at least) is at least moderately charismatic. Not enough so that I must take speech/barter, but enough so that I don't want to bring it too low.
And I think I would put the luck, because I will rely heavily on critical hits (which is partly why I want Lucky).
On the critical hit front, be sure to get 6 points into Perception, for the Better Criticals perk. It will give you +50% more critical hit damage, which is huge. Guns, Sneak, Lockpick and 45 pts only in Melee Weaps for Cowboy perk. And definitely get Hand Loader, as there is no armor-piercing ammo available for revolvers, without that perk. And you will need that kind of ammo often.
I understand the Hollywood desire to be 'charismatic'... every gunslinger wants to be the dashing movie-star type who gets all the chicks and looks good doing it, right? Um, well... the problem with dreaming that the Charisma stat in NV will somehow do this for you... is that it's just that- only a dream. Charisma don't do squat for you in the game. It's only real benefit, is if you want your companions to do all your fighting for you- then Charisma is the stat for you. Otherwise, it's practically useless. Better off to use those valuable stat points elsewhere. Before you get to lvl 40, presuming you will play the DLC, you'll have more skill points than you know what to do with, so don't bother worrying about the few points extra you'd get in barter/speech, from Charisma. It just really is no big deal.
Agility is a good stat to max out for any guns char, and particularly handguns- it affects reload speed, run speed, amount of AP, and several other important things I can't remember just this moment.
As for other perks, how do you intend to play your gunslinger in combat? Are you going to use a lot of VATS, or are you going to try honing your twitch skills and do as much freehanding as possible? Several things to consider- if you stick to revolvers, you will have very limited ammo to start each fight with, before having to reload. In my experience, if you fight freehand, you will miss a whole lot more than if you use VATS. So, you will end up doing a lot less damage per cylinder, getting beat up a lot more, and probably dying a lot more. If you go with VATS, and take the Gunslinger and The Professional perks (and later on Sniper, which works for handguns as well as rifles, and enables successful headshots much farther away), you will be a killing machine, no two ways about it.
If you choose the VATS route, get as much AP as you can, I prefer Kamikaze trait, Action Boy/Girl x2, and maxed Agility. Enough AP to net you at least 4 VATS shots with the Ranger Sequoia (30x4=120+ AP needed). You can get up to 135 AP if you build for it, which will give you a full 6 VATS shots with the Mysterious Magnum. Pretty sweet.
There will be a lot of folks who will snicker at using VATS, but before you decide how to go, consider this- if you want to use primarily six-shooters, what will your average fight look like? Not counting the singles or pairs of mobs you will run into, which are easy for most any character... no, I refer to the 3+ sized groups that are the real test of what your build can do. You have six shots. You will have to get in close and undetected, unless you want them to be blasting you from range and making your life hell. You want to be able to take out as many of them as possible, as fast as possible, from close range and by surprise, before they have a chance to rush you and kick your bum. And remember- there are no silenced revolvers... so once you fire the first shot, it's on for keeps.
So- high sneak is a must. And probably fighting mostly at night, to make the odds even better for your close-range way of life. And killing as many of them as possible before they crawl into your shorts. I'm sure you can see where I've been going with this... do you feel lucky? Are you an uber twitch freehand shooter who can headshot 4-5 mobs with only 6 shots, at really close range, with them running and bouncing willy-nilly all over the place and trying to give you a vasectomy without the benefit of anesthesia? Good luck, dude. I may freehand the first 1-2 shots, from stealth- going for free headshots before they have a chance to rush, and saving some AP. But once the charge is on, VATS quick.
VATS definitely has its uses, and a revolver build, where you need to make every shot count, sure as heck is one of them