Both of these Mainboards are of high quality with lots of features and great overclocking potential. The main difference between them is that the Gigabyte Z790 AORUS MASTER is bigger. It is an ATX-E Board so it is wider than standard ATX Boards. This has to be taken into account when choosing a case for your PC.

yes it's E-ATX, it measures just 1.6 cm more width though. It fitted quite nicely in my Fractal s7 compact despite not supporting E-ATX form factor.