Open your console F1 and type this commands:
render.level 0.0
grass.on false
grass.forceredraw False
grass.displacement False
grass.disp_trail_seconds 0
grass.shadowcast False
grass.shadowreceive False
gfx.ssaa False
gfx.bloom False
gfx.grain False
gfx.ssao False
gfx.shafts False
gfx.tonemap False
This will help you get more FPS

Other commands:
terrian.idleinterval 0
render.af 0
render.aa 0
env.clouds false

I use only grass.on false and render.level 0.0 because you dont gonna have lags and game still look beautifully.