Nowhere could I find out how to get Sweetfx working with thief, but alas, I figured it out.
-Drop all sweetfx files including (but only one of) the Reshade Dll's (Reshade32.Dll and Reshade64.DLL) to:
64 bit users -username\steamapps\common\Thief\Binaries2\Win64.
32 Bit users -
-Now rename the Reshade .DLL to "dxgi.dll" if running DX10 or DX11. Rename it to "D3D9.dll" if running DX9. (The instructions are in the readme in the main Sweetfx folder)
Now, right click .exe "shipping-thiefgame" and check "run as administrator" under compatibility tab. Boot up game. You should see a prompt in white acknowledging that Reshade is working and installed properly
Here is the clutch move - For some reason in this game you need to enable in game SSAA. The graphical anomalies in the main menu should disappear when you enable SSAA. They did for me anyway...
Remember: only use Reshade32.dll or Reshade64.dll depending on which version you are running, make sure to rename it after copied, and copy sweetfx files into Binaries 2 not Binaries.
I hope this helps someone else out there
Enjoy this Preset by Proudi- https://sfx.thelazy.net/games/preset/3846/