I did these while we were playing bridge this afternoon. We were near large windows so the shutter speed is high, but the back of the room is dark. A7R2 with set to Av, center weighted metering, and the ISO was set to 6400, 12800 and 25600. First 6400. No Lightroom adjustments. Then 12800 and 25600 The fact that the camera set high shutter speed because of luminance doesn't distract from the high ISO performance.