Wow, you upgraded from a cropped sensor camera to the EOS-1D X. That's quite a jump up. Yes, the High ISO capability on the 1D X is really amazing. Look at this shot I took in Paris a couple of months ago. It was taken handheld @ ISO 6400 f/4 with the EF 24-105mm L lens. The image is heavily cropped because I was about one mile away, on top of a high rise building on a hill.
