I am on 10 frame Langstroths and very happy with them. And asking about 8 frame poly was a combination of some recent ponderings.
One pondering was about experimenting with some poly boxes to get a feel for what they are like.
The other pondering was using one size box with langs probably works quite well with 8 frame. A narrower taller cavity (with single, double or even triple brood) slightly closer to that of a tree, and better insulation. And totally interchangeable frames without ending up with a top box of honey weighing a metric f^@*tonne.
The 8 frame boxes of honey would be somewhat easier to handle than a full size lang. I'm still strong enough, but it's not the most joyful of weightlifting.
If bees do prefer working more vertically in a better insulated cavity... this might be a way.
Anyway, it's an unlikely experiment, and quite often my boxes have 9 frames in them anyway.
B
p.s.
I'm in australia at the moment, and although I haven't actually got involved with any beekeeping while here, I see apiaries allll over the place, and I seem to see pretty much exclusively stacks of white wooden 8 frame deep langs with migratory covers.
I appreciate that the climate here is somewhat different.
(and they still don't have varroa... seriously... wtf... it must change beekeeping so much!)