Well, the 27 isn't the fastest lens of the bunch, and it doesn't have stabilization, so here's what I'd probably try if I were going to a club to get pictures...
1. In situations where you can't really use a flash, maybe crank the ISO to 6400, and shoot RAW+JPG in Black and White, so the noise looks a little more "charming." In that mode, I would be dictating 6400 and f2.8, and then letting the camera speed up the shutter as much as possible, because people have a habit of moving around at bars and clubs. I'd also be bracing that camera on something as much as possible - I've used the top of my pint glass countless times, for example.
2. Flash or no flash, if you find yourself in a situation where you're going to shoot someone who isn't moving around from one spot (a singer in a band, someone standing at the bar waiting, etc), then make sure you lock that focus down and then just WATCH, waiting with the shutter already half pressed down, watching for good facial expressions to hit the shutter button. Take the focus part out of the equation for the camera. I sometimes forget to, and then the camera has to hunt again for each shutter press, inevitably missing a few.
3. With Flash... I haven't used flash a ton in those situations, because I don't want to stick out or be noticed. I see you can sync it up to 1/180, just like the XT1, so I would have the camera in full manual and be making little adjustments as I went to account for subject distance. if, say, 1/60 and f2.8 and ISO 3200 was working well, and then things got darker or the subject got farther from the flash, I'd use the shutter speed dial up top to slow the shutter down. See, you're getting punished a little here by not having the XT's ISO dial up top, AND by using the only lens in the whole XF lineup that doesn't have an aperture ring, so adjustments on the fly aren't going to be as easy for you.
I'm not much help. Use black & white, crank the ISO, and let it hunt up the shutter speed scale as far as it can. Oh and don't be afraid to drop the EV comp a little, to help your capture a little, and then boost mids a little in post to make up for it?