Basically i have a gigabyte gtx 670,ga-z77x-ud5h motherboard, 16 gb corsair vengeance ram,i7 3770k,I run 3d mark and it says my computer is not quite enough to be high performance gaming pc, I wanna change that now do i buy another gtx 670 and sli them or just go and buy the gtx 690 will it be worth the extra money for the gtx 690 and will i have a high performance gaming pc,