With the exception of the fothergilla, all of the listed plants will rapidly exceed the space requirements and none of them are benefitted from frequent pruning to keep in bounds. It is far more desireable to select a plant that will not easily exceed the size limitations of the site you have in mind, rather than relying on pruning to keep it to size. I'd also question how well a deciduous, shrub-like plant will come across as a "specimen" plant. I'd consider dwarf conifers. First, in our climate you have an enormous selection of these to choose from and a great many are produced by nationally recognized growers in this area. Many dwarf Hinoki or Lawson cypress are easily within your size restrictions and offer a very wide range of shapes, textures and foliage color. I'd also consider upright junipers, like 'Gray Gleam', 'Moonglow', or Witchita Blue'. These offer wonderful foliage color and although they may eventually exceed your size requirements, they are more easily pruned and shaped to remain within the desired size.

It was recommended I post the question here as well. Thanks for the help.

Collector's has a wonderful display garden . I will be in Louisville tomorrow and I think I will take Mike Hayman a 'Silver Cardinal' . Mike is a tree geek who has transformed his neighborhood into an arboretum . I would think 'Silver Cardinal would have better hardiness . I think it would definitely be worth trying doniki , there are so many variables . People tell me all the time that something won't grow here . Well I like to try and succeed . If your not killing you are not growing as a gardener . Maples of any kind can be tricky . Some of the literature I have read has 'Silver Cardinal' as syn. Acer x conspicuum like Bboy said . It is odd that it would not be zone 5 . Anyways A. pseudo. 'Brilliantisimum' , 'Eskimo Sunset' or A. pictum 'Hoshi yadori' should all be hardy in zone 5 . Good luck .

As you can see the top tree seems to have smaller leaves. It is closer to a silver maple than the bottom. Bottom's leaves are much larger and greener. Both were planted at same time in fall of last year. The top tree, has pushed more new growth this season, which seems to be indicative of stress? I may prune these to get that classic shape later on. A couple low hanging branches and one or two parallel's. On the whole, after this season im gonna let em do their thing.