Not sure if this has been posted here before, but I was messing around with some of the Frostbite console commands and I noticed that:
PostProcess.DynamicAOEnable 0
Netted me around 10 FPS in random Hinterlands areas (not near camps, those are still framerate death traps). I figured this was just turning off Ambient Occlusion, but that requires a game restart to take effect, and the effect of this command can be seen in real time.
Nevertheless, I manually disabled Ambient Occlusion in the settings and restarted my game just to see what would happen. I gained a few FPS, but nothing major. I ran the command again, though, and my FPS shot up 10+ again.
So I guess you could give this command a try. It obviously makes ambient lighting look worse.