Nice discussion.

Here is another very important issue to think about: in order to get more volume (that is at a certain level) you need a lot more watts to achieve a audible difference.

300 watts or 400 watts don't make much of an audible difference at all. Try it if you don't believe me.

Or try this: turn up your volume knob on your KB very slowly to about 2/3. You'll a here a noticeable difference in volume with each increment.
Then turn it up all the way. Not much difference.

Regarding the overheating problem: I own 3 Mackie SRM450, 2 for the audience, 1 as a monitor.
We just had an outdoor gig at a french festival. It was very hot and we played at a good volume. No overheating noted.
The Mackies are clean and loud.
As far as I remember, Uncle Dave is the only one who had that problem in the past, with a speaker that was placed on the floor.
Corect me if I'm wrong.

I still give the Mackies 2 thumbs up
But of course only with the 9000Pro

Eric