I am in a different zone than you, but I had mine in south/southwest location and I had too much winter damage. I had to cut it back severely two winters in a row. I moved it to a more protected spot and it is doing great, even this past winter when many other broadleaf evergreens had problems. Design-wise, I'm no expert, but one on each ends seems too formal for what looks like a casual area. I don't follow what you meant by downplay the height if they get 20' tall. You might get better design input on the landscape design forum.

A Blue Prince may be a bit smaller than the stallion. My 3 Lady's have Princes. http://www.skh.com/NurseryPdf/holly.pdf

there are 3 problems with overwintering in z5-6 .... the key is.. GET IT DORMANT>> AND KEEP IT DORMANT .... if you put them in a structure.. there is a chance they will come out of dormancy and start actively growing weeks or months before proper .... so that is problematic ... also.. they can get too dry ... its hard to water in winter in our zones ... if you do NOT protect them.. then you have issues of water build up in the pots.. and freezing the root mass solid ... and also.. winter sun on black pots ... can freeze/thaw the root mass too often ... all that said.. rather perfunctorily ... the best tempering device you have.. is mother earth .... she will hide the pot.. and she will provide water on those warmer days ... i dont really understand why you cant plant them now .... even.. as noted above.. if you just dig a hole.. and sink the pot and all in the veggie garden ... they can be moved and planted properly as soon as the soil thaws in spring .... IF YOUR SOIL HAS PROPER DRAINAGE... if you have horrible clay ... well .... figure out how not to sink it into a cauldron that does not drain ... if all else fails .... set them on the north side of a structure .... absolutely no sun .... let them go dormant .... and then around 1/1 ... lay them flat on the ground.. so that water can not accumulate in the pot ... to put a sharp end on it... just planting them.. 95% success rate healing them in ... with or w/o pot [no clay] .. 90% north side, tipped over .... 89% unheated structure .. in my experience .. 80% good luck ken

Here's a few off the top of my head that might fit the need. I picked some large hostas since you are trying to replace Sum and Substance. None of these get quite that large though. Blue with gold edge: Tokudama Flavorcircinalis - An oldie but goodie Brave Amherst Wooly Mammoth Aristocrat - Very bright These ones have more of a cream to white margin: El Nino Regal Splendor First Frost You can see pictures of these at the hosta library but I would go to the hosta forum on Garden Web and serch for other pictures as well. Hope this helps. Here is a link that might be useful: Hosta Library