Its an amazing camera in low light. I have tested up to 3200 and it is amazing, I would say that shooting night and interiors under natural lighting will be a strong point of this camera. Its auto white balance seems to be very accurate as well. Great colours and sharpness under mixed lighting.
So one of the great benefits of the X1D is the shutter in the lens- turn day into night shooting at 1/2000 of a second with the little Metz on camera flash. Bit harsh but a great look in black and white. I have to say, under this light EVERY crease and wrinkle pops out so maybe not one for the self conscious, heaps of character and coupled with the 50mp sensor it is pretty mind blowing.
The X1D does kick ass monochrome, new firmware is a big improvement. The camera has the potential to be a modern classic, already it produces outstanding images.
Johnnyshoots 