Steve,
can I ask what you mean by Poplar. A very few I find turn-able. Most poplars I can get hold of are like turning cotton wool. Certainly I've not seen the grain/ring structure I can make out on your piece before. Is it one of the American ones?
And I've not seen the other option for a finial, but this one sits very well and I can see why it was chosen, but I think I would have continued the curve of the line below the bead through to the part above the bead.