Thank you all for somegreat advice.
As an experiment, I bench tested SLV and Firestorm using my Intel HD 4000 on board adaptor on the same parcel that had some trees and fine grass. Here is a summary of the settings in each...
Quality bar = between high and ultra
Advanced lighting on, but no shadows
No ambient occlusion
Draw distance: FS 600m, SLV 512 m (this was the max from what I could see)
Hardware settings : Anisotropic Filtering on, Open Gl Vertex buffer on, Streamed VBO's on, Antialisaing disabled.
Results: FS has an acceptable 12 - 30 fps. SLV couldn't even move, the screen wouldn't even refresh for me to see the FS meter change.
So to say that I'm pleased FS has saved me $200 on an NVIDIA video card is putting it mildly !