I have both. Ilove my m9 in all respects. But, the x 100 has much less grain at ISO's > 800. Also, the fill in built in flash on the x100 at night is far superior to the SF 24D on my M9. Maybe my opinion would change my mind if I had a Noctilux. But with summilux 21,50,and 75 mm, the x 100 is superior in very dark situations. In brighter situations, the x100 tends to suffer from glare, lacks sharpness wide open, and lacks the sense of depth that a Leica lens provides.