Seemingly scentless, yet a true butterfly magnet!

Later blooming than the common varieties.

Pretty tall even with occasional topping - right now at about 12'.

Leaves are elliptical and coarse-textured.

Any ideas?

After quite a bit of searching, I now believe this to be Syringa prestoniae 'Donald Wyman'.

Bloom type, set of blooming branches, bloom color, bloom season, leaf type, height of plant, availability at time of planting; and lastly, the reports of as many butterflies as blooms on any given day are all the same.