Some seem to be forgetting NVIDIA does employ technology to smooth SLI, whether this be frame rate, or frame time, I do not know, but the fact is NVIDIA uses technology to do some sort of smoothing. That is simply a fact.
Some people are more sensitive to detecting smoothness/consistency differences between SLI and CrossFireX. Like any other human sense, there are varying degrees of sensativity. Some people can detect it, while others cannot. It is analogous to FPS, some people are sensative to FPS over 60 FPS, and some simply don't feel it.
But the fact remains that NVIDIA is doing something to make SLI smoother in gameplay experience, this is known information.
So when I say I "feel" it, perhaps feel is a bad descriptive word (but it is lack of a better description that exists), it is a combination of my eyesight/brain/mouse/keyboard input, all wrapped up together that translates to "feeling" different. Descriptive word aside, you put it all together, and it all points to the same conclusion.