Ended up picking up a used copy of Fuji X-Pro 1 as my sneaky solution to “no professional cameras allowed” situations without compromising all too much at the end of the day, and overall I am quite impressed with this combo considering price:performance ratio you get out of it today.
The obvious thing just about any camera lacks in low-light is decent autofocus, especially with an f/2.8 lens or slower (and Fuji actually optimized the 27mm to be a true f/2.8 on a crop sensor rather than having the x1.5 crop factor with the aperture as well), but contrast detection of the X-Pro 1 definitely lags behind Nikon’s phase detection (and it’s ironic considering that X-Pro 1 is a rangefinder-style digital, what the phase detection was based on in the first place). Manual focus works nicely with digital viewfinder zoom/peaking aids, but at a fast-paced music environment this is really the last resort, especially on mirrorless cameras.
The bread-winner of the Fuji is very appealing grain in high-ISO images, thus virtually no noise that I would normally be quick to remove even at the expense of some sharpness (which would be a problem for the 16MP sensor in Fuji unlike the 24MP + full frame sensor on my D600). Without further adieu, here are my edited and cropped/web-sized jpegs from the RAWs: