Using a Canon 1Ds body, I compared the results of a photo shot from a Leica 50mm Summicron-R with a Novoflex Leica-to-Canon adapter with the same photo shot from a Canon 50mm f1.4 AF lens. By no means scientific, but both photos were shot with the camera on a steady tripod, on a cloudy day. Both lenses were set to f8. I might revisit the experiment with additional data points in the future, but until then, here are the results.

This first photo is the image shot with each lens. It was a cloudy day and the shutter speed was 1/60th sec., so a tripod was essential.

This image is from a small slice of the photo taken by the Canon lens.

This image is from a similar slice of the photo taken by the Leica lens. The Canon 1Ds was set to aperature preferred exposure and allowed to set its own shutter speed.

Conclusion:
From looking at the comparisons, it appears that at f8, both lenses are comparable in performance. The long distance object was rendered with similar sharpness, contrast and color.
I invite any comments. Please email them to me at photo-m7@comcast.net .
Happy Shooting!
John Gong