Gaming PC for my old Steam games collection. I plan to play mainly old games that I did not have the chance of playing when they were released, at 1080p 120 Hz and the highest quality settings. Those games range anywhere from Portal 1+2, Bioshock 1+2, The Witcher 2, GTA V, or NBA 2K13, and also many less demanding games like Trine, King's Bounty, Bastion, EVE Online or EU IV. For those games, the GTX 770 is probing to be rock solid with stable 110-150 fps.
Also the PC is going to be used as a media server for the home. I used to have a 4-Bay NAS, but I grew tired of it. Torrent downloading was not reliable, and I had many problems with my unit, so after 2 years of constant pains, I asked for a refund. Those four WD Red 3 TB will house a huge library of multimedia content and also provide a much reassuring backup for important data. They are stripped in pairs, and copying large files from one volume to the other works at 254 MB/second. On the NAS, on RAID 10, I never got even close to 50 MB/second.
I am really glad of the performance I am getting from this computer. Right now I have not overclocked anything because I feel that I do not really need it. When I start playing more demanding games I may change my mind.