Buildings & trees flickering

Following the advised tweaks for cfs.config, I set composite terrain texture pool, Composite aircraft texture pool, Vertex Buffer pool and Index Buffer pool from default to SYSTEMMEM. Now I get buildings and trees flashing on and off. If I set them back to default, then everything is fine. Anyone else getting this?
The unticked Dual Pass Render and ticked High resolution Z-buffer tweak works perfectly.
My motherboard is a 1 Gig Epox NForce 4, with AMD64 3400 and a 256 mb GeForce 6800 GT Graphics card. I'm running Direct X 9.0c.
The unticked Dual Pass Render and ticked High resolution Z-buffer tweak works perfectly.
My motherboard is a 1 Gig Epox NForce 4, with AMD64 3400 and a 256 mb GeForce 6800 GT Graphics card. I'm running Direct X 9.0c.