This game is pretty much an Alpha when looking at the patch notes and changes all the time. At the moment their "nerfing" allot on the GPU which is a good thing which should give improvement. Although this game is leaning allot on NVIDIA Engines such as Physix and rendering methods. Since you got a Radeon R9 it should not be much of a problem.
Most of the times with my beastly specs (listed below) I also have quite some GPU and CPU lag from the game.
PC Specs:
- Asus Z97-K (Mainboard)
- Intel i7 4790-K @ 4.812 GHz
- Corsair Vengeance 2100 MHz 2x 8GB (16 GB In total)
- GeForce GTX 980
- Other Parts not listed because of of irrelevance.
As for more information it is the best to daily check
this page for the latest patch notes and updates of the game. As you will see they are improving allot and adding it on the fly. Ark is one of the only games where I am actually satisfied with how they produce patch notes and updates.