As much as I like the Physx stuff and such I find the same thing happening so I disabled grass and such, esp shadows. I do find now though that trees seem to get in the way more as I like to play zoomed all the way out.
BTW, Love the forums it has helped me greatly and got me into HC. Though I'm US bound I play with a D.A.R.K. almost nightly, he has been very helpful.
Thanks!