I/O bracket for all models is a 2-slot bracket. This will allow for a slightly wider card to fit in cases that some people had difficulty with on the 20-Series 2.75 slot cards.
Thickness of the 3090/3080 XC3 models with backplate (XC3 Ultra/XC3) is 1.78in. - 45.1mm.
Thickness of the 3090/3080 XC3 models without backplate (XC3 Black) is 1.61in. - 40.9mm.
Thickness of the 3090/3080 FTW3 models with backplate (i.e. all of them) is 2.19in. - 55.55mm.
Thickness of the 3090/3080 FTW3 models without backplate (manually remove) is 2.02in. - 51.35mm.
https://forums.evga.com/Introducing-the-EVGA-GeForce-RTX-30-Series-with-iCX3-Technology-m3072847-p11.aspx#3073427