It looks like you didn't watch the video JohnnyGoo. The reviewer had a 40 watt tube Marshall 12" speaker, that wouldn't keep up with drums. But the Orange 35RT with the 10' speaker did. Why would it need a 12' No i don't think so..
So what you’re suggesting is. Contrary to everything we’ve been led to believe…. Size really doesn’t matter?
There are several variables in the loudness of a speaker. One important factor is speaker sensitivity. The more sensitive a speaker is, the more effectively it uses the input signal supplied to it, meaning there is less loss. The more sensitive speaker will be louder for a given input level than the less sensitive speaker.
Now, size does matter in terms of the overall sound pressure level (SPL) the speaker is able to produce. But, theoretically, a more sensitive speaker that pushes harder can overcome its size deficit and produce a greater SPL than a less efficient, though larger speaker (depending on how much different the sensitivity is). This is also affected by the sheer mass that has to be moved by the voice coil.
One other factor is frequency response. A 10" speaker generally will have a frequency response that is more mid-forward than a 12" speaker (this can vary quite a bit, however, depending on other construction characteristics of the speaker). It just so happens, human beings are more sensitive to mid range frequencies that lower frequencies. So, even with the same SPL, a more mid-focused sound will be perceived as louder, even if it isn't. This is simply because we hear the mids better.
Just a couple of things that make ya go, "Hmmm."
Of course, when I go, "Hmmm," I generally follow it up with, "....I think I need a V."
Which, is yet another thing that may make ya go, "Hmmm."