The lighting inside Mayfair's well-heeled "Whiskey Mist" bar was frankly appalling. Unable to use flash, I ended up relying on two lights erected either side of the small stage by the videographer (who at the last moment was barred from actually recording the event!) Nonetheless, I still had to push my camera farther than I was really comfortable with, dialling up the sensor's sensitivity to dangerously noisy levels.
Maintaining focus was a huge problem. My Canon 5DMkI's autofocus simply couldn't cut it, certainly not with a wildly animated performer in such dim conditions. I was also shooting wide open with a wafer thin depth of field. Centimetres, literally. In the fraction of a second between me locking focus and squeezing the shutter button, Johnny more often than not had slipped out of focus.
Although I bristle at the suggestion of using technology to fix a problem which may in fact be one of technique, it was quite clear that having a more sensitive autofocus and a selection of f1.2 primes would have helped enormously. A hotshoe-mounted AF-assist light would have come in mighty handy too.