SLI is good for high end GPUs, but if you do it with the likes of 7750, 7770, 7850, GTX 650, 650 ti
microstutter might be a huge issue. For the money that you would spend it would be much better
to get a single higher performance card.
If you are trying to say the 7850 is a low end card then you are mistaken it beats the 6950 and with a small overclock it reaches the speed of a 7870.