That's not really overkill for anything. If anything you could go bigger (not size wise but with storage performance). Personally I don't bother with the WD blacks as they're overrated. They're not even the fastest HDDs out there. I use Toshibas across the board as they're much cheaper and just as reliable in the end. You can look in to RAID options on your mobo (assuming you're using a RAID capable mobo).
If you're building brand new I'd stick with Z170 though, which opens up even more capabilities and expandability.