I think the mansfield beech would look better in terms of contrast. Of course, it's easier for me to visualize because my M40s are in beech. Have you thought of a custom finish? The russian maple is almost the same tone as the beech with a bit more grain. With the custom samples you at least get a nice sized plaque to compare against. I would say order some samples, even the standard finish and see how they look. If you're gonna do it, do it right.

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"Nothin' up my sleeve. . ." --Bullwinkle J. Moose