Tested v290.10, nothing changed.
Anyway, I just found what causes those fps lags on my computer. It's LOD applied on trees.
I suspect it's caused not only by trees, but everything which LOD have an effect on, as rocks, bushes, birdges, structures...
See the video, preferably in HD:
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http://www.youtube.com/watch?v=QnfcXNrtctU
As you can see on video, when I move nearer or away from trees, LOD acts: new 3D model of trees (their shape and texture changes) and then, my fps become choppy and I experience lag until everything is displayed, then fps gets back to a stable rate.
Surak!! help!!