Indeed. But it was reflecting on some of your thoughts that made me choose a 4R 2x12. I knew that two 2x12 8R cabs would be twice as powerful, but also that a single 8R 2x12 would be half as powerful (more or less).
I had the sense to realise that if I was ever in the situation of needing two cabs then that would only be because there was a big pa which would make big backline redundant anyway.
The extra headroom/power offered by 4R wasn't really needed (or so I thought) but in practice has opened the door to a greater choice of options as I can use lower power amps.
I would also say speaker efficiency trumps everything. A quality speaker that has a good wide range response and is 8 to 10 dB more efficient will be louder and more flexible with more headroom than any practical increase in amp power. And probably mord reliable as you won't have to work it so hard.