Steve,
It looks great. I'm not really qualified to comment, as I know enough to know what it takes to do something like that, but can't myself do it. If I could do something like that, I'd be thrilled... might even put down my tools and walk away, having mastered a form. The idea that you're trying to make it even better leaves me stunned in awe...
Having said that... this seems like a classical (or neo-classical) form. If that's the case, the standard guide for proportion in such a piece is the golden ratio. Way too much math for my tired little brain, but you can read the details here:
http://en.wikipedia.org/wiki/Golden_ratio
It's a pretty interesting subject as one digs deep into it. A few choice snippets:
Beginning in the Renaissance, a body of literature on the aesthetics of the golden ratio has developed. As a result, architects, artists, book designers, and others have been encouraged to use the golden ratio in the dimensional relationships of their works. (...)
Studies by psychologists, starting with Fechner, have been devised to test the idea that the golden ratio plays a role in human perception of beauty.(...)
Adolf Zeising, whose main interests were mathematics and philosophy, found the golden ratio expressed in the arrangement of branches along the stems of plants and of veins in leaves. He extended his research to the skeletons of animals and the branchings of their veins and nerves, to the proportions of chemical compounds and the geometry of crystals, even to the use of proportion in artistic endeavors. In these phenomena he saw the golden ratio operating as a universal law.
The article was clearly written by an academic, so that every assertion has a qualifier, and there are copious notes and references. One could drown in the subject.
It would be interesting, although perhaps bootless, to see if viewers preferred a finial on your piece which approximates the ratio. All I can say is it looks awfully good to me!
Thanks,
Bill