I used a 4-shot 39 MP back for years. It did a great job with film formats ranging from 110 to 8 X 10. I used a modified Polaroid MP-4 copy stand (XL column) and rigged up a strobe backlight using an Elinchrom Quadra and a small Chimera soft box with some opal glass thrown into the mix for extra diffusion. The results were stunning, and the light was even throughout the field. I had a sweet X, Y, R compound for moving film larger than 645--useful for precise stitching. The ranger provided more than ample light and it was great dialing the power on the strobe instead of changing f/stops on the lens. That way, I was always able to use the the best aperture and didn't have to touch the lens for bracketing exposures. The entire rig, without camera, strobe, and soft box came in under $1,250 (including an anthro cart to anchor the copy stand). I shot tethered and focused remotely without touching the lens.
Hasselblad's multi-shot solutions are used at the treasury dept, Harvard, Boston Public Library, Boston Museum of Fine Art, and tons of other museums and gov't. institutions. There are lots of ways to skin a cat when it comes to hi-res digital capture of flat media. I'm surprised the guy at the NY public library wasn't handling the original art with gloves. Oh well...