I have a Gigabyte UD3P-EP45, it has two PCI slots, one being a x16 and one being a x8. I'm wondering if i can go SLI with two x16 cards. Will a x16 card safely fit into a x8 slot? I understand that if so, the bandwith wouldn't be as high, but i don't mind that.
Yes you can, no worries at all, the card will work either slot just fine. And read the article on the front page of Toms this week about PCIe slot bandwidth, you may be pleasantly surprised to learn 8X bandwidth is only very, very, slightly slower. Not enough difference to even be concerned about.