Why does selecting YCrCb 422 in the GUI not seem to have any effect in the Hardware?
There were some issues reported in the Vivado 2015.4 DisplayPort v6.1 (Rev. 1) GUI.
This issue is resolved in Vivado 2016.1. Please see (Xilinx Answer 66301) for a patch for the DisplayPort v6.1 (Rev. 1) in Vivado 2015.4.