I realize your specific question was about the 20D, but I'm going to assume that we can stretch the definition of this thread a bit. I have M7s and an RZ system and shot MF Velvia and ISO 100 negative film for two years before buying a 1Ds. Since mint-condition prices on the 1Ds are now quite low, I'd wager that you would consider this option vs. the 20D if you're thinking about a decent MF scanner to compliment your M7 system, which isn't inexpensive.
I've done exhibits with 20x24 prints from MF, scanned with an Imacon drum scanner, and displayed them side-by-side with 20x30s from the 1Ds, all printed on the Epson 7600. They look very comparable at typical viewing distances.
I think a very telling conclusion is that my M7, a great system with exceptional lenses, now stays at home -- and I'm shooting 100% digital. The reason for this boils down to three key advantages for an all-digital solution: Workflow and image processing convenience; overall flexibility of a system that spans WA to telephoto to macro needs; and overall quality in printed output. And, the quality side of the equation will only get better with the 1Ds Mark II.
Two other comments: Buy the very best lenses with the 1Ds-class body, and invest in your image-processing technique (RAW conversion, Photoshop skills, printing, etc.) Do these things, and I think for most people, you won't look back.