It would be the same if it was 700 lights affecting one single object. That's the beauty of deferred rendering, and this has some tricks to make it even faster.

I don't know about Hummel's particular code, but deferred shading can be done taking advantage of MRTs as early as shader model 2.

In fact, since 3DGS uses DirectX 9, it couldn't possibly require a shader model 4 card.

Deferred shading isn't performance hungry at all -- that's the whole point of it. And that's why you can have hundreds of lights affecting each object.

Jibb