BP10B can be had for $400ea ($500 retail ea). 20Hz-20kHz @-5dB per Julian Hirsch at Stereo Review Lab.
B&W 684 for $500ea. -6dB at 34Hz-50kHz
Monitor Audio RS6 for $500ea. FR 38Hz - 30KHz(only spec I could find)
Polk Audio RTi A5 for $475ea. -3dB 40Hz-26kHz
MB Quart QLS830 can be had for $500ea($849 retail ea). FR 33Hz-32kHz(only spec I could find).
MB Quart likes to quote you the OVERALL frequency response, like Def Tech.
You have to search for actual lab numbers. For example, the MB Quart Alexxa S-1 ($900 retail ea.) is MEASURED to have a low frequency response of 51 Hz @ -3dB. However, on their website, they quote as 33Hz-32kHz.
http://www.mbquart.com/all/downloads/testberichte/Stereoplay_11_06_AS_Sone_en.pdf
Another example: The DT BP7000SC is listed as 11 Hz - 30 kHz. But actual lab numbers are 20 Hz - 30 kHz -3dB (90dB reference).
So on paper, the BP10B blows all those speakers out of the water. On paper.
Now in some rooms, the BP10B may NOT sound as good as the MB Quart. In other rooms, the MB Quart may not sound as good as the BP10B. It goes the same with all speakers. That's why we all know how important audition is and how important acoustic room treatment is. But on paper, the BP10B blows them away.
My gut feeling is that if you take 20 speakers that cost $500, chances are they will all sound very similar and very good. It may differ only in personal preference. But on paper based on those mentioned specs, the BP10B blows them all away.