Yuk.. My new 5D3 has to go into the shop. So Im going to rent a 1Dx for this weekends wedding.. Gonna test it shot for shot against the 5D3's especially very dark reception lighting and Dance floor shots. So,, i will get a report to you guys next week. Big Country has both and notes that the 1Dx is usable at 20000 iso right off the camera...so im gonna find out. Will also put the newer AF features to test against the 5D3 and see what we get.