I'm planning on building my first PC within a week or two and completely clueless on how many PCI Express 3.0 x16 slots I will need on my motherboard. I plan on getting a single GTX 980 now which is a dual slot and uses up more space. If I were to use SLI in the future, how many slots would I need to be able to run SLI? Would I need two slots on my motherboard or three since a dual slot card takes up an addition space?