Very high GDDR usage

Hey guys,while I´m on another round of "squeeze-the-hell-out-of-this"-tweaking (You know what I mean.) I tried the setting BufferPools=0 instead of RejecetThreshold and I clearly got an FPS boost and less shutters but now my GFX card´s RAM is almost fully used (max was 1011 of 1024 MB, average on 850 - 950MB) and the GPU usage is arround 70-80% with spikes up to the high 90-ies. Is that ok or is that usage limiting in any way?