The MSI RX 470 8GB does not support SLI. It supports crossfire. SLI is specific to NVidia. The GTX970 is faster than the RX-470 but due to the memory configuration, may run into issues in games that need more than 3.5GB of VRAM. The 8GB of VRAM on the RX-470 gives it a little more longevity in that regard, however, complaints are common place for Crossfire. I would suggest going with a GTX1080 as opposed to SLI with a pair of GTX970's or Crossfire with a pair of RX-470s....