Hey there, Bradley!
Have you considered getting a NAS? This way you will prevent your PC from being ON all the time, while the NAS takes up that responsibility. You will also be able to access it all the time and to connect it with your plex server and gaming PC.
When we are talking about 24/7 running drives, WD Red drives are indeed the solution.
They have the TLER feature (time-limited error recovery), which prevents the RAID/NAS configuration from dying and saving you from rebuilding it every time a drive failure occurs.
http://www.wdc.com/en/products/products.aspx?id=810
Since your PC build is all about gaming, there I'd put a WD Black drive.
This drive is designed for demanding applications and gaming, giving you fast write/read speed. It is pretty fast with 7200 RPM and 64 cache that will deliver quite the gaming performance.
http://www.wdc.com/en/products/products.aspx?id=760
Having a NAS with WD Reds and a gaming PC with WD Black, you will have everything connected with access to all your data, without sacrificing your gaming performance.
Let me know if you have any questions!
SuperSoph_WD