Because Intel only provides two miserable ports, why do you think?
Um, no. Only storage access will be at all slower, and then only if forced to flush before the next read, whilst having a high QD...IoW, something that just doesn't happen on 99.9% of desktops. Get the single drive, and realize that you're obsessing too much about nothing.If you run Windows in SATA II, the following will run in SATA II mode such as: Directx 11, GPU drivers, internet/wan/lan drivers, audio/sound drivers, virtual memory, online communication headsets & anything else that windows need to run your games. It feels crippled.