Which one for real-time 4K in after, nvidia qaudro k5000 or Titan Z, or something else?
My PC is X-99, i7-5820k, 64GB, raid0, SSD...
Surely you jest. AE has never, EVER been realtime. It's not designed to be realtime.
Dream on, pal.
In it's current state rendering in After Effects is mostly CPU so graphics cards make little difference in performance. Adobe usually (but there are no guarantees) announces updates at NAB which is in a couple of weeks so I would hold off buying any new hardware, especially expensive hardware, until you see the new system requirements and release dates for the new versions.