I feel like I should be getting better performance than I am. I am usually between 40-50 FPS but get drops down to 30-35 sometimes. I am trying to figure out if it's a driver issue, an issue with the Linux version of POE or something else. My CPU usage rarely gets as high as 80% on a few cores and when it does my FPS is fine. My entire RAM usage doesn't go above 2.5GB. I am using the latest driver for my GPU. I got better performance from Crysis 3, The Witcher 2 and Far Cry 3 which in my opinion should be the more demanding games. Any ideas ?

My system has the following:

AMD FX-8350 @ 4.5 Ghz | 12GB DDR3-1600 CL10 | Club 3D Radeon R9 280X 3GB | OCZ 128GB Vertex 4 SSD | Linux Mint 17.2 64 bit

Basically it comes down to the fact that Unity is trash but extremely approachable for developers. The game runs extremely poorly for what it is no matter what your rig is normally capable of because it's built on a horribly inefficient engine.
I get similar problems with every Unity-powered game I own.

Not true. My rig is not half the beast of the OP's, and I get no issues whatsoever, and the same goes for other Unity games I play, like Shadowrun and Wasteland 2.

Unity'll run on everything, but it won't run well on anything. Pillars of Eternity puts actual load on my GTX 960 and has absolutely no right to - however, it runs about the same on my work notebook which is kind of crap.

That depends on your interpretation of "won't run well". I'm not an FPS whore, and I find no issues with the engine. I daresay putting it under a lens will reveal things the average user (me) is not even aware of.

Eh, it makes my GPU hotter than it should be given what it has to render, I'm not really complaining about performance per se. I believe the engine rendered even fully 2D graphics in a completely 3D environment - last time I checked the official unity tutorials, they achieved parallax scrolling effects by literally putting different layers of background further back on the z-axis. Might be different now tho, they were supposed to optimize the 2D rendering a fair bit in the meantime.

According to Steam (GoG version launched through, as Steam is the only FPS counter I have) game generally runs at ~40 FPS in most areas with occasional drops to 30 and peaks above 50 on my "Witcher 3 ultra ready" rig (okay, almost, I have 2 R9 290x instead of 980, but PoE can't into Crossfire). So I don't think it's something on your end.
However, in terms of resources consumption PoE is very modest - in comparison Wasteland 2 (both vanilla and DC) look worse, yet consumes much more of everything, especially RAM, up to 14 Gb. PoE places almost no load on my PC. The only troublesome area now is loading times, especially first load after game's launch, even on SSD it takes a lot of time, so I transferred game to my rather fast HDD instead.

Well I'm going to run an experiment and figure this out. I am downloading POE on my Windows 7 partition and am going to play for a bit on that. We'll see what the FPS diffrence is like. If I am getting a huge boost on Windows then it will be down to drivers and Linux optimizations on the game's part but if it is just as bad then we'll know maybe it is Unity.

It's the Linux drivers, Pillars doesn't run very well with the proprietary AMD driver, but it is stable at least.

I found it ran better with the open source drivers, but then it was always crashing during certain areas of the game.

I just went back to playing it on Windows too.