As I’ve got the 8RE version of the GS65 here it means that it’s got Nvidia 1060 graphics, while the Aero 15x has 1070 Max-Q graphics, so another important difference that will affect performance, however the 8RF version of the GS65 is also available with 1070 Max-Q graphics, so assuming you’re looking at that model in theory the performance differences shouldn’t be that drastic between the two.
I saw this review: Aero 15x vs MSI GS65
So which of these two laptops would you guys pick?