How big are 5770s??? which case/motherboard?

So i am thinking about getting the MSI 790X-G45 AM3 AMD 790X ATX AMD Motherboard with a quadcore 955 black edition and am also thinking about a crosshair formula III motherboard. I heard the 5770 was huge and i dont wanna lose any slots. I am getting a antec 902 case so im hoping two of these guys wil fit without problems. now i see that the formula has dual x16 and doesnt display them as 8x by 8x. I know thats prob what they marketers who do new eggs summarys meant but why do some say one at 16x and the other at 16x whereas others say 16x 1 or 8x 8x 2? sorry i have a hard time explaing but i hope u understand. Which motherboard should i get, the formula is freaking pricy and i wanna overclock but to pay THAT much more money than the msi, motherboard selection help too, THANKS A BUNCH   oh yeah and how BIG are those 5770s. which board would fit two better in a antec 902!