I really like Shenandoah, but none of the ones I have grown have foliage as tall as Heavy Metal, which will be at least a foot taller. Something to think about if you really want that extra height. In this planting, I'd probably choose Heavy Metal.

Have you considered Calamagrostis Karl Foerster? It will be about 4 ft in foliage and taller in flower. A little fuller looking in seedhead and a good backdrop and compliment to Perovskia.

Remember that this planting will be dormant during winter and not provide year-round hiding of the utilities.

I'm new to this grasses forum but can't help weighing in on this, although you may have already made your plantings. grass-guy makes a great point about these grasses dying back in winter. I would forget about the perennials in the first instance. Some appropriate and strategically placed conifers (most of which are evergreen) in various colors might work nicely. You could then use any grasses you like to compliment your conifers. If this interests you go over to the conifers forum, give them your situation, and ask for conifer cultivar tips. I've just ordered some 'Shenandoah' by the way and am really looking forward to growing it.