No, they can't SLI. Lowest Nvidia card that can SLI is GTX 1070. Also, don't forget to check if your motherboard supports 220W processors if you want FX 9590, and if your CPU cooler supports 220W processors, too. I don't much suggest to upgrade to FX 9590, because they have issues with overheating and underclocking, it's better to upgrade from FX 8300 to 8370. If you already have that, you can try to overclock it, FX can easily overclock to 4.5 GHz.