this is a still on going built of mine. You can find a worklog at bit-tech: http://forums.bit-tech.net/showthread.php?t=273891
I will edit lots of details here next week why I choose which parts and so on :)
CPU choice: A i5 4690k would have been enough but I choose to go the enthusiast way and to go big. I bought this selected i7 Monster which is highly overclockable. You can find a OC screenshot in the Gallery. With this beast I will manage 4k gaming at High settings.
Thermal Compound: It's good compound and pretty cheap therefore I went with it.
Motherbord: I started with this Project last year there I bought the z87x-oc. After Devils Canyon was released. I sold the old Model and bought the new OC beauty. GA is not known to have boards which reduces Vcore (there are more used for Ln2 benching), but the Orange is just too eye catching than to go with a usuall red/black
Memory: It is a highly overclockable DDR3 Ram. It comes with Samsung chips on it which are pretty good :).
Storage: I've got a ton of Data which wants to be stored. I could buy a huge stock of those Seagate HDD. I am still not sure if I use them in this project or not. I may build a NAS in the further Future ( still don't know). The Crucial Mx100s are the best SSD when you compare Price/performance. The Samsung Evos are pretty good,too but in day to day work you will not realize any difference. My choice here isn't still fixed. I may go with bigger once if I choose to build a NAs for storage.
Graphics: Well everyone know that one 970 isn't enough for 4k Gaming. Therefore I will get a SLI. I will buy only GPUs from EVGA because everything in this rig will be watercooled.
Case: I fell in love with the Corsair 900D. The only one who was complaining about it was the Mailman cause the Case is just huge :)
PSU: I neede a silent, but powerfull PSU which had to be Full modular cause I will make my own wire and sleeving. I tested a lot of PSUs, went to the Cebit in Hannover (germany) and then choose the Antec HCP 850.
Monitor: I still got an Dual Monitor setup. In the near Future I will add a thid one which will be a 4k Monitor.
Fans: Fans fans fans, I neede a **** load of them to stack them on the rads in push/pull. With that I get decent silent cooling power.