The new NVIDIA drivers seem to help, especially with Ambient Occlusion. Yesterday I could barely hit 50 FPS. Now, I'm getting a stable 60 FPS at 1200p with the following settings:
Origin In-Game: Disabled
Mesh Quality: Ultra
Shadow Quality: Ultra
Texture: Ultra
Tessellation: High
Terrain: High
Vegetation: High
Water Effects: Medium
Post Process Quality = Ultra
Post Process AA = High
Ambient Occlusion = SSAO
Effect Quality = High
MSAA = Off
The bolded settings seemed to have the greatest impact on FPS with my setup:
i7-2600k
GTX 670
8 GB RAM
Windows 8
If anyone else is having trouble, I highly recommend dialing down the Effects setting and disabling HBAO. Lowering the Mesh, Shadow, Texture, and Tessellation settings provided small performance gains compared to the bolded settings.
EDIT
I'm taking this brief opportunity to state that the above post is all bullshit. Once I hit the Hinterlands, I had to dial down just about everything. I left Mesh and Texture quality at Ultra, left HBAO on, Tessellation at low, and reduced just about every other setting to its lowest. Whatever, 70 hours in and I'm enjoying it so far.