Actually SLI is seldom, if ever, used for rendering. Although Nvidia does have the "gelatto" renderer that is accelerated by graphics card functions, it's not used in very many actual production situations. TV at best, certainly not film. It's just not up to the level of quality necessary. So any SLI setups for a workstation *are* used to accelerate the viewports (3D realtime views of the model/scene), and not for actual rendering.
- Oshyan