Will TWO of these GTS graphic boards fit in my mobo?

i would think that nvidia would have designed this board so you would have no trouble getting two even three dual slot graphics cards in your only issue is your SATA connectors are in the way do you get a long sli connector with your mobo you could put the second gts in the third pci-e slot and have access to 3 SATA connectors but then you couldnt use the bottom pci slot and depending on what hardware you might decide to put in the slot between the 2nd and 3rd pci-e slots it might hit the sli connector. the southbridge heatsink should be low enough to give you clearance.

absolutely they will fit. even if you go with the top white and the top yellow, you will have room, tight, but there is an open slot between them 2 to give you the room you need for the big cooler.

as mentioned, nvidia designed the reference for the mobo, as well as the video card. you know the mobo (as long as it follows nvidia's guidelines) will hold the cards without issue.