I think the problem once you get into the higher flow rates that the fan design can't help with is the amazing amount of air that is "wooshing"....moving very quickly, through the system. It is less a fan problem with many of the fans and more of the nature of the volume of air. Even top-notch bearings and a great blade design are hard to make these quiet at the higher air flows.
Do you have room to put more fans which you can run at a lower speed, instead of a few very high speed and flow fans? Could you duct/reposition/etc your setup so you don't need as much air, as long as it is used more efficiently?
You are right, maybe that is the wrong approach, so far I'm impressed with Gentle Typhoon AP15, very quiet but still great amount of air flow, just bought several more and will stick to those for a while