i have a b75 motherboard and a hd 7770 if i was to crossfire (add another graphics card) wat would be the best? it has an extra 2.0 pci-e runs @4 so it wont have it's full potential but still would allow me a bit more power. the exact specs on the website = Slots: 1x PCI-Express 3.0 x16 Slot; 1x PCI-Express 2.0 x16 Slot (runs at x4); 2x PCI-Express 2.0 x1 Slots; 3x PCI slots
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Sell your 7770 and get a higher end card like the 7870. Crossfiring two lower end cards like the 7770 won't get you any where except for more power usage and tons of stuttering.
pcie x4 v2 is insufficient for hd7770, hd7770 will not be able to show its true power
so it is better to sell and go for higher end single card