Yes, it is. For example, in my own experience, Maxwell GPUs frequently do not post with SandyBridge CPUs on some X79 motherboards (Asus P9X79E-WS is one). The

Yes, it is. For example, in my own experience, Maxwell GPUs frequently do not post with SandyBridge CPUs on some X79 motherboards (Asus P9X79E-WS is one). There are BIOS fixes for this, but many of those motherboards were discontinued before NVIDIA GTX 980 in September of 2014. Ripping out the SandyBridge CPU and replacing it with an IvyBridge CPU magically fixes the problem. I think the difference here is that SandyBridge only supports PCIE Gen 2 while IvyBridge is PCIE Gen 3. One will never know for sure though.