Will x2 HD 7950s fit on my Micro ATX Maximus IV gene-z/gen3??

Yes they will fit and unfortunatly that will be all you will be able to fit as they will cover the bottom x4 slot. The two full x16 slots are pci-e 3.0 so when Ivy Bridge comes out and you want to switch to one of those then you will be able to utilize the Pci-e 3.0 with the slot , video card and cpu all being pci-e 3.0 complient.