Conditions you described will be adequate for Elegantissima to prosper if you'll remove some cinnamon ferns from planting zone to let cornus roots get established.
I have it in a less sun + maple root competition and it providing me with what I was looking for: bright variegation on a tall plant in a shade. It's about 6'+ tall and 4' wide from 18" twigs in a 3 years.
In a more favorable conditions probably will be taller and wider, but I'm happy with it as is.

I am unwilling to remove the Cinnamon ferns but the place I want to site the Cornus is presently lawn and I won't have to remove anything except sod! I am sick of mowing the area (it's awkward) and have allowed Mr. Mower and my easy operation of it to dictate the amount of lawn that will be "sacrificed" for the dogwood and some more Hydrangeas (maybe).

I was concerned about sunlight for the shrub, but the site has been sunlit since about 3PM and it's now nearly 5Pm and the sun is still on the site. Thank you for your thoughts, if you have more to offer... well, I'm "all ears"!

>I don't have a really good book on shrubs (the Dirr book should arrive via Amazon in a few weeks)After which you'll have to keep looking.

Timber Press DOGWOODS book prefers to call it 'Argenteo-marginata', says in description of this particular one "White-margined leaves...are moderately susceptible to leaf spot". Discussion of variegated Cornus alba in general says "Numerous variegated and gold-foliaged forms are available. Some make excellent garden specimens; however, they need to be sited with care in some climates. In areas with hot summers and intense sun, the variegation can burn in a very nasty way. Partial shade is quite welcome in these areas. In addition, many of these cultivars show fairly heavy susceptibility to spot anthracnose which can render the foliage quite putrid by midsummer. This malady seems to be far less problematic in the Pacific Northwest. In the eastern, midwestern, and southern United States, it can be downright scary. Good garden sanitation is the gardener's only reasonable weapon in this regard. Variation in cultivar susceptibility is noted in the cultivar descriptions [as above]."

I've always clipped mine a little. This year I haven't done it and it is between 5-6' high but less than 4' wide. It will get higher if I let it go. It grows on the North side of the house in fast draining sandy loam. Not sure if it gets any direct sun in the summer but its happy. As these shrubs age, they loose their red stem color so some people prune out 1/3 of the oldest stems each year. Mine haven't done this yet but I see commercial plantings let go that hardly have any color left at the base. Other people just cut them back hard to control the size. It looks crappy at first but the plant fills in by the end of the season.
There has been at least a couple of posts over the years here about leaf scorch on new plantings. They seem to do this for some people the first year or two and then grow out of it.

my 2 cents worth - I have 5 of these that are probably 10 years old. They get the brunt of mid day sun with early morning and late afternoon and evening shade, situated in less than desirable soil that tends to get rather dry and they have been perfect plants. No scorch, no spot anthracnose(sp?), very good variegated color, and bright red winter stems. I cut them back every other spring to get rid of the old wood that tends not to color up much in the winter. How it will perform in your situation could be different.

I'm really glad I checked back! Thanks for the encouragement on the Dirr book, bboy. ;) Oh well... every library has to have its "dogs", right?

I think I'm going to give it a whirl. The site is mostly shaded, very moist, the plant won't set me back much, and looks wonderfully healthy in spite of having endured 1-2 winters in its pot. If it sucks, I yank it out (I've gotten quite brave about such actions of late).

I wondered why the stems weren't very red, and now I know. I'll remember the prune back 1/3 advice, as one of the reasons I like the plant are the red stems in winter. And, I'm a sucker for varigated leaves, too.

Bboy makes no secret of not really liking Dirr, but my feeling is that it's one of the best books around for this part of the country, though it may not be for the west coast.

I have one planted in my shady backyard - I don't even think it gets any direct sun at all in the summer months when the leaves are out on our 'forest' of maples (lol). I just planted it there as an experiment, and it's turned out really well. Brightens up the shady spot... I have it planted in a bed with rhododendron, azalea, brunnera, hosta, etc. I say, go for it - can't hurt to give it a whirl!