I have always used deep Mann Lake Plastic Frames for brood. I started with them because of the perceived small cell advantage - my thoughts at the time were small cell might or might not help but I'll take any edge I can; It couldn't do any harm, and they were cheap.
I noticed that they were, and still are, often sealed to the frames above and below. Michael Bush was gracious enough to explain that despite appropriate bee space between boxes they probably burred them together because they didn't see the top of the PF frame as a barrier like they do with a wooden frame - if I recall correctly - that the thickness of the wooden frames top bar helped stop them making contiguous vertical comb as they do with a PF.
I have got used to working them and I like them for brood, not so much for extracting but that's another story.

My main observation, and thought in starting this thread, is that the honey stored in a PF frame because of the thin (nearly non-existant) top bar extends almost to the very top of the hive, and that when the comb is empty bees can cluster in those empty cells at the top. I am wondering if this helps the cluster when compared to the traditional wooden frame with its thick wooden topbar? In a wild colony there is no topbar at the top of the broodnest just cells. Does the top of a cluster in a hive with PF's have an advantage in retaining heat? When compared to a wooden framed hive, the bees can pack together more closely at the top and have more points of contact with honey? Would this allow survival of a smaller cluster - all other things being equal?

I have about 430 Mann Lake PF deep frames in my hives now, and no plans to buy any wooden ones. I am curious if anyone is running colonies in both types of frames and has noticed any differences, or has any thoughts, about my above musings.