I too was looking intently on purchasing this camera, but since I do a lot of wedding videography without extra lights, I have decided to wait. Because the CMOS chips are only 1/4" they have less surface area to capture light. The smaller, 62mm, lens doesn't help the situation either.
But, the only real way to tell is to challenge the camera. Place it in a dark setting, say a 12'x12' room with a single 60watt light bulb in the middle. Then put the camera on a tripod and shoot some wide angle and zoom shots of some books on a table. First set the camera to auto mode. Then manually set the iris to full open (F1.6?) and the shutter to 1/30 and the gain to 0. Then change the gain to its highest setting (18db?). Then compare the images. If you want, I would be happy to do the same with my Z1U and we can compare to see what kind of difference, if any, there is.