I am reminded here of the time when I did some drag reduction on an aircraft that the owner of the kit company felt was snake oil.  He proclaimed loudly and to everyone present (6 owners of this type) that I was full of s--- and virtually demanded that the improvements be removed.  The owner of the now 10 KTAS faster aircraft merely shrugged and said:

"But Alan, it's faster!"

The effects of a prop switch are complex and without going into it all I can say that most of the assumptions I have seen quoted here on the original prop's qualities are in error and incomplete as are most of the equations being used to quantify the comparison.  If the prop in the real world made that much difference, then it is not the new owner's responsibility to mathematically "prove" his performance.  We have races for that.  If anyone wants to try to quantify this on paper and comes up with anything but the actual flight test numbers (within allowable test errors), then they either have inaccurate data, assumptions, and/or equations.

This experiment worked.  My congratulations to the owner and Hartzell.  Is it worth the extra cost and weight?  Only the individual owner can answer that.

Eric Ahlstrom