Species name arboreum and common name tree rhododendron tell the story. If you want an emphasis on verticality that is the one to plant. Flowering commences while still comparatively small.

Many other rhododendrons grow tall in time but most are more shrubby in character. Quite large ones often still have the stems dispersed so as to appear as a giant bush. The tree rhododendron grows with a conical shape for many years, almost in the manner of a conifer, and is one of the tallest-growing species.

None will get big overnight, the largest wild examples are hundreds of years old.

Tree rhododendron flowers sometimes very early in the year and is therefore not suited to locations with recurring spring frosts. Flower color ranges from white to blood red. Subsp. delavayi is usually this last color.

Thank you! Since I saw such a stunning specimen very nearby, and it's on the ARS list for my area, I have high hopes for R. arboreum. (And if anybody out there is visiting San Francisco in the near future, you've got to check this thing out. Maybe I'm easily impressed, but...)

I can be patient, it seems to me that most rhododendrons grow fairly slowly.

Not that many climates where such plants can be grown, so if you have the interest and the space...

Site conditions, including human activities and local regulations permitting if you want to really put on a show plant a row of them as street trees.

Here is a link that might be useful: rhododendron arboreum - Google Image Search

Interesting, I don't doubt that this could be an R. arboreum but I'm surprised the habit isn't more upright, unless you've been pruning it. Granted I haven't grown one to maturity but most of the garden pictures I've seen depict very upright grown rhododendrons. My small one I have in a pot for breeding has had very strong apical dominance. In the Bay area I saw scads of them for sale at Berkeley Horticultural Nursery and Sonoma Horticultural Nursery (unrelated) that had been pruned into a tree shape, in fact it appeared to be the only way they are sold.

Doesn't look like a pure R. arboreum to me, instead one of many rather blowsy and gaudy hybrid rhododendron cultivars in bloom everywhere in the region at this time. And R. arboreum has been used in hybridizing for a long time, this might be something that has R. arboreum in its parentage and therefore got the name attached to it wherever you got the plant. Otherwise it seems R. arboreum seeds gathered from a collection could yield hybrid seedlings even if gathered from plants that were true R. arboreum. Supposedly a big motivation for establishing a collection of bona fide wild rhododendron species at what became the Rhododendron Species Garden in Federal Way was hybrid seedlings being grown under species names.