Tested out the leaked version. Just in case, here's proof that I've got a legal copy of the game already.
I was downloading a game on Steam in the background, so I'm not sure if that would've affected performance in a significant way.
Specs are GTX 770 2GB, i7 4770K (with turbo boost to 3.9GHz), 16GB RAM and Windows 7. Game generally runs well maxed out at 1080p, with FOV set to +10. Maintains 60fps for the most part, with some minor dips here and there. I ended up setting distance scaling to medium instead of high, as I noticed some strange drops around Cassardis. Roughly the same amount of pop-in with the medium setting as on high, with 10% less GPU usage. Generally quite high GPU usage overall on my machine, with CPU usage barely going much higher than around 20%.
Speaking of Cassardis, the room you start off in is quite weird performance-wise. Looking in a particular direction results in a drop to 55fps (which is eliminated if distance scaling is set to medium), yet that drop isn't present if I exit the room and look in the same direction.
FXAA isn't particularly well-implemented IMO. Makes the game noticeably blurry, and there's still a lot of shimmering on distant objects.
Perfectly fine performance:
Suddenly drops after slightly rotating the camera:
Looking in the same direction right outside:
Distance scaling set to medium: