Hi Chris,
It’s a great question! As you correctly state, HDBaseT is designed to work on unshielded Cat5e cabling, and in fact that is the cable used when products are sent to our test facility for certified testing. Of course, using a higher grade cable (such as 6a) brings benefits in terms of signal immunity and crosstalk reduction, which really come into play when bundling HDBaseT links together. If using 5e in a bundle, we have a number of recommendations that apply to the first 20 meters from the Transmitter, such as not pinstriping/combing the cables, not pulling cable ties tightly, etc. When moving to higher grade cables, these recommendations are relaxed.
From my experience of talking with the installer community, most are pulling Cat6a (or even Cat 7). This is exactly for the reason you stated – that they prefer the additional margins in their installation which come at a negligable on-cost for the better cable.
Like you, I would be happy to hear more comments from participants in this forum…
Daniel