Hi,
Awesome example! It's just the kind of thing that I want to be able to offer my clients.
Yes, I suppose 6 images can get really frustrating if a lot of post work is required. For these primitive tests that I have made, I've been mainly trying to maximize image quality (apart from the obvious lack of resolution) and minimize distortion. In an actual production I will definitely consider a spherical render!
I think I also need to be a little more careful on my material settings if I am to render 6k images ;)