Ho hum this gets fun when they let the sales guys write the tech manuals...
According to this you've got 38 lanes total
http://en.wikipedia.org/wiki/AMD_900_chipset_seriesBut then according to gigabyte product page, the full length slots run at 2x16 or 4x8...
Whatever, that's 32 accounted for. 6 left... unless they do try to get 2x16 and 2x4 then we've hit 40... there's supposed to be an additional 4 lanes due to the northbridge, but I was getting the impression they were internal to the motherboard, for the gigabit LAN etc... if it uses one and leaves three, that's your 40, and one 1x slot working and that's it...
Well you can bug gigabyte on it, but they'll say it supports 4 GPU period.