As per the specifications from SapphireTech.
Sapphire HD 7970 GHz Vapor-X Edition is a GHz Edition card. It has two variants, one 3GB & another 6GB. It features a non reference PCB [not a standard PCB made during HD7970 design] with 8-Phase Power Design. It runs at 1000/1050(Boost) MHz Core Clock & supports 1 x HDMI (with 3D), 1 x Single-Link DVI-D, 1 x DisplayPort 1.2 & 1 x Dual-Link DVI-I. Maximum you can drive 3-monitors out of both.
Whereas cards like Sapphire HD 7970 GHz Toxic Edition, features similar specs but drives 4-monitors at a time. It's a 6GB Frame Buffer variant with pretty hefty GPU Cooler [sapphire calls it Toxic edition]. It supports Default: 1050/1100(Boost)/ Lethal Boost: 1100/1200(Boost) MHz Core Clock MHz Core Clock & can drive 1 x HDMI, 2 x Mini-DisplayPort, 1 x Single-Link DVI-D, 1 x Dual-Link DVI-I.
Boost & Factory OC cards are not GHz editions from Sapphire.