I've just built myself a new machine because rendering times on my laptop were prohibitive. It's an i7900 10 core processor, 32GB RAM and two Quadro P4 graphics cards with 8GB memory each. The cards are set up to run together under NVIDIA's SLI configuration and Blender recognises them both for GPU rendering.
Whilst rendering times have improved dramatically, Blender rarely uses more than 10% of the CPU and no more than 50% (rarely) of one graphics card. The other one just sits there gathering dust with the odd 2% contribution according to the system monitor.
My question is: why doesn't Blender use more of the kit? It seems to me I should be getting blazing performance with the extra capacity but it never breaks sweat.
Incidentally, I have an animated sequence of 1300 identical spheres falling under gravity and the viewport grinds to a halt whilst CPU does almost nothing - it doesn't update between frames and Blender doesn't respond seemingly due to working hard on calcs. I don't get it.
Am i missing something?
Screen shots as suggested.