Hey,
I just wanted to tell you, that the new 27" iMac 5k Retina iMac is not working properly with 10.11.1 because of missing Skylake drivers.
For example the USB ports don't work correctly. External storage drives do not connect at all or maybe only on one port with very slow (2.0) speed.
It has a special build 15A4310 if 10.11.0 on it. Which seems only to be available over Internet Recovery. Downloading El Capitan from the AppStore is not possible.