I have a 295 with the 3D vision and scaling seems fantastic in some games, not so hot in others. In most games you WILL take around a 50% hit to your framerate, so keep that in mind. Unless you're getting over 100fps in games before you turn on 3D it's not worth turning on. You really notice the lack of frame rate in 3D, remember 50fps=25fps each eye. Not enough to make the game appear smooth in 3D. Thankfully with all the console ports out, it's not too much of an issue if you have a fairly decent setup.
Some games however I turn on 3D and only get around 25-30% frame rate loss. No idea if the SLI is just scaling better or what, never really looked to hard into it.
If you have any other questions feel free to ask. I've been playing around with the 3D vision for nearly a year now. It's definitely amazing in some games, not so suited for others.