Several years ago, Bob Lemon and I debated the merits of hammer-rail
lift versus key-bed shift to soften or change the tonal expression on
a Duo-Art.  Bob opted for the lift, I opted for a shift on a Steck
Duo-Art Grand.  We ended up doing both.  I could have it either way.

Later we had the same decision to make on a 6'6" Steinway Duo-Art.
On that one we opted for the hammer rail lift as it "seemed" to sound
better.

The bottom line?  I believe one's course of action hinges upon personal
preference.  In my case there are two examples, where one piano sounds
better one way while the other is reversed.  Go Figure...

Ray Bauer

 [ I feel that it's because of the "unpredictable" effect of the keybed
 [ shift; different pianos yield different volume suppression.  So
 [ you're quite correct about experimenting for the best result!
 [  -- Robbie