Hi Dram. Sorry for the delay, I've been busy.
Affirmative, lowering Grass LOD in options cleary helps, but mouse control still looks choppy and inaccurate. Activating vsync and triple buffering at driver level improves performance a bit.
I've also experienced low frame rates on Mars while using multi-camera vehicles (up to 6 on medium rovers). It looks like my graphic card can not ride the overload of so much shaders running in the background, so I put offline most of them while moving around in 3rd person view.
Thanks for your help.