Sky Pencil Holly - Zone 5B Hardy?

I came across these Sky Pencil Holly at Fast-Growing-Trees.com (that's where the photo above is from) and I found myself going down a Sky-Pencil-Holly-rabbit-hole to figure out if we could grow these in the Chicago Suburbs (Zone 5B).  The folks at Fast Growing Trees list them to be hardy down to zone 5B.  But the team at the Missouri Botanic Garden list them down to Zone 6. 

These things are super narrow and grow perfectly upright, so they have a lot of appeal to me.  But, I'm afraid that multiple sources (besides the folks who are selling them!) are concurring about Zone 6 hardiness.   Check out the video here:



In particular, I was thinking about them alongside the north property line, in front of the fence where our (eventual) walkway would direct people back.  Check out this area I've circled in red on our landscape plan.  It is a tight area that would call for something very slender, yet would provide a sense of 'entrance. 

These Sky Pencil Holly would be perfect, I think, but alas they weren't meant to be.  Maybe we'll go with a set of arborvitae or something else narrow and tall.  The one thing we have going for us on this side is time.  I'm thinking that I can plant something small this Spring and over time, allow it to fill in the space and mature. 

In our old house in Elmhurst, I ended up planting a couple of flowering pears that grew pretty upright in a space like this.  I had a little bit more space away from the property line in that instance, so it made more sense.  I really liked the way that it created that sense of enclosure and made it feel a little bit more cozy as you entered our backyard.

One consideration right now is that the walkway that you see in the drawing above isn't there yet.  It is planned, but isn't there.  Perhaps, I could 'jog' the sidewalk to accommodate a larger planting? Or maybe there's something else we can do that isn't the Sky Pencil Holly or a flowering pear, but has the same characteristics?