A user on Steam posted a temporary fix that helped me out quite a bit. Go into your binaries folder, rename Win64 to "Win64Backup" for example. Copy Win32 and rename it Win64. Forcing the game to run in Win32 doubled my FPS and caused less shutter.

I find this game to be a little strange on the performance side. The first day, it ran flawless. Second day was crazy FPS issues, and it's been back in forth ever since. Once I did what I posted above, the problems have gone away.

I'm running 660 TI OC SLI, so any Nvidia users out there, give this a shot and hopefully it works for you.

Nice to know, thanks for sharing. I'll try that.

I'm getting a pretty solid 60fps on my HD 7950, but more performance is always better. The game looks fantastic and runs smooth already for me, but if I could turn on SSAA and consistently get 60fps that would be great.

From what I have seen the Nvidia cards have lower minimum framerates on this game than AMD cards do.

I've seen quite a few GTX 770 benchmarks, for example, and they always had much lower minimum fps than I do.

Here is the results of one typical GTX 770 benchmark for Thief:
Min. FPS - 16.8
Max. FPS - 64.5
AVG. FPS - 50.7

Here are my Thief benchmarks results using my HD 7950:

Min. FPS - 32.1
Max. FPS - 60.2
AVG. FPS - 43.3

This is with all settings completely maxed out including high SSAA. The benchmark is synthetic and not necessarily indicative of in-game performance in any case.

As we can see the GTX 770 produces great average framerates, but the minimum framerate is a lot lower than the HD 7950 achieves. I don't know if this is specific to the benchmark or indicative of performance in general, but it might explain why some with Nvidia cards are saying their performance isn't great.

If that is the case, hopefully Nvidia can improve performance in their next driver release.

I wonder what could cause the changing performance from day to day. Did they release several updates that I was unaware of?

Come to think of it, though, I had the same experience. The game ran flawlessly the first day I played it, but later I saw dips down into the 50s a few places. Maybe it is just because I reached new locations in the game that were more taxing.

You should try the Sniper Elite games, so good, especially with coop

Same here. I'm glad there are some other people who enjoy these types of games!

@isarai I tried Sniper Elite 5 and ended up really enjoying that one. Went back and played 4 as well!.