Probaby the most stunning viburnum when in flower is the doublefile - Shasta, Mariesii, etc. IMO, few other viburnum species come close to being as attractive or anywhere near 'specimen' status. But these are not small plants, do not take well to pruning (it alters their very tiered, layered growth habit) and can get quite wide - 10-12' or more.

I am very partial to my Nantuckets, a hybrid developed by the National Arboretum in D.C. They are almost evergreen in my zone (6b), with dark glossy leaves. The shape is dense vase shape. The flowers are like Carlessi but regretfully without its fragrance. If fragrance is what you want, go with Carlessi! It too has a kempt shape, more globular than vase, and dark but not glossy leaves.

few other viburnum species come close to being … anywhere near 'specimen' status

But these are not small plants, do not take well to pruning (it alters their ... layered growth habit) and can get quite wide

Yes and yes.

However if you can find or order in V. plicatum f. tomentosum 'Summer Snowflake' (same species as 'Shasta') that one naturally produces a compact narrow habit. And continues to have some flowering after the main event in May. So if you are sitting out on the patio during summer the shrub will have something going on in addition to habit and foliage.

Would have to question just how 'compact' and 'narrow' 'Summer Snowflake' really is. While it does form a more rounded shape, IME these get almost as wide as a regular doublefile, if not AS wide. One near me was 15' across before it got cut back severely! And while it does have a longer bloom season, it lacks the incredible in-full-flower impact of the standard doublefile that makes it such a show stopper.

Would have to question just how 'compact' and 'narrow' 'Summer Snowflake' really is. While it does form a more rounded shape, IME these get almost as wide

I've seen tall old ones that were nearly columnar, formed (in part) the basis for my comments. (Small potted stock often has the same habit also). Meanwhile pictures on the web show a mixture of straight-sided and spreading plants under the same name:

https://www.bing.com/images/search?q=viburnum+summer+snowflake&qpvt=viburnum+summer+snowflake&FORM=IGRE

Would that have anything to do with your location, GardenGal? Where I am in south-central Indiana (so fairly near the OP), the largest 'Summer Snowflake' I have seen was 10-11 feet tall but only about 4 feet wide (no pruning). Shorter ones have been similar in width. Am I just seeing less mature specimens?

I'm not sure I can answer that :-) Both of the ones I've seen with a wide growth habit were very mature plants......20+ y.o. But even younger ones seem to grow rather widely as well. Most online resources (MOBOT, Monrovia, etc) will state a mature spread half again as wide as tall.

Maybe I should have clarified...I don't necessarily need something more compact. My patio will have a 12' circular bed at each corner, however there will be no barriers...so I can move the planting out more and expand the bed outwards as it grows. 12'-15' mature growth is no problem. I see various mature viburnums in my area...some have nicer, tight forms and some have gawky and loose forms, however I'm not well versed in what cultivars I'm looking at. Maybe viburnum is not something I want as a focal points on the patio? Or maybe a cluster of 3 smaller growing specimens?