What speakers play the loudest cleanly ?

For a non-horn type design, I would say that the larger ATC are the loudest and most dynamic speakers you can find. The ATC 3" midrange has a much bigger magnet than 99% of woofers (just to give you an idea). ATC woofers also use heavy magnets and have some of the largest Xmax I know of. Watching Top Gun with ATC is like being there on the deck of an aircraft carrier...either you need ear defenders or you need to turn down the volume to a comfortable level. These speakers are not suited for a condo.

klipschorns, jbl vintage ie jubal etc, bose 901's(802's) , westlake audio....other pro designs

I'm part of what appears to be a very, very small camp who thinks if one focuses first on proper line conditioning, vibration management, interconnects, and speaker cables, you may find that far more speakers will play clean at even extreme volumes.

-IMO

I was suprised to see someone with enough nerve to nominate Bose 901s, but they are correct. I had a double stack being fed by 500 watts a channel that were capable of producing nightclub sound levels without breaking up.

Big horns, hands down. If you had a pair of Avantgarde Trios with a few stacked pairs of their Basshorns...