Tim,
Proper setup is probably what sounds good on the SME and as pointed out by Thom your effective length probably matches what the spec should be. "I suspect he's getting such good results with a Wally because his cartridge's stylus position closely matches SME's design assumptions, and therfore his tonearm's effective length is close to specification"
I just thought I'd bring up some other points as food for thought. I have not yet decided which way to go for a set up tool.
One other point, I think some of the changes we make are so small as to not be detectable from one to the other by using the arc, even with a magnifying glass they might look the same, so probably sound the same.
Mike