"Watts are watts, and they are calculated the same way", is absolutely true. It is also true that efficient speakers require fewer watts. While these are electronic facts, "watts are watts" is not an "audio fact". For reasons unknown to me, that apparently can not be explained; "tube watts" are bigger stronger and tougher.With tubes in a push/pull configuration they generally have more current available. I had a Bryston B100sst rated at 180w @4ohms. I now have an Octave V70SE tube integrated rated at 70w @4ohms. The Octave just destroys the Bryston in terms of 'control'. My speakers are Dyn C1 signatures rated at 85db. For solid state the Naim line has great current capabilities for the low watt rating.
That's been my experience so far :)