The way I was taught to use a scanner, scanning at over 100% quickly starts destroying "image quality". I always scan at 100%, and adjust other parameters (ppi, etc.) to fine tune the actual size of the image. If I ever needed it larger, I would upsample in a dedicated program like Genuine Fractals, not when I scan. However, I have never needed to scan at more than 100% at 4,000 ppi for a desired print.
However, I'd ask at HybridPhoto.com, not here. You will get better answers and tick off fewer people.