Coming to this thread late, but I have been working on a project where I have been doing close-up photos of tattoos, looking at the interplay between the pattern of the ink and the texture of the skin. The subject is usually curved, and the total magnification to the final print is generally on the order of 10X. I have used 35mm, 6x6, and 4x5 and have gotten decent images from all 3 formats, but depending on the particular subject sometimes one system works better than others.
If my subject is relatively flat (for example, a tattoo on a back), then I tend to prefer the 4x5 where I can adjust the plane of focus to have more control over what I have in focus vs what is thrown out of focus. Otherwise, I have tended to like using one of the smaller formats where more of my total magnification is coming during the printing stage.
One of the other considerations that I have is the exposure time - since my subjects are alive, and don't remain completely still, faster shutter speeds are better, and when I am using L.F., because of more magnification to the negative, I am forced to longer exposures.