These are the main performance murderers:
Grass (Set to High), Extended Distance Scalling (max 20%) and Shadows (but it's worth on very high).
I run at 1080p and it rarely (if ever) drops below 60fps. I have everything maxed except for Grass, Extended Distance Scalling, Reflections (High, not worth at Ultra and Ambient Occlusion (worthless and affects performance). I use FXAA+TXAA+MFAA (nvidia control panel) at 2X.
I have a GTX 970 btw. Read this...