frequency response - B&W vs. Monitor Audio


I currently have a pair of B&W 685s and I am considering replacing them with a pair of Monitor Audio BR2s. The MAs freq resp gets down to 42Hz; the B&Ws only get down to 49Hz. Is this an audible difference? I would be getting the MAs through a friend who has access to wholesale prices and I will not be able to audition the MAs.
2nd issue - I am considering high-passing my bookshelfs through an active crossover in a powered sub. This will cut out frequencies below 80Hz before the signal gets to the amp and the bookshelfs. If I do this, does it matter if I upgrade to the MAs? Their high end is 30kHz, the B&Ws high end is only 22kHz. Thanks.
realremo
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Dylanhenry-, there must be a reason why speakers (tweeters) go way beyond the human ear for defining a positive musical note and ampfliers to take the Musical Fidelity amp the 'Titan'(just as an example as I sure all amps go way beyond 20khz) can hit nearly 100khz, now the human ear because we do not have the hearing of a dolphin, or even an elephant, we hear very high khz 'Harmonics' way above 20khz, which is what every musical note has, which is and I quote;

'Any of a series of musical tones whose frequencies are integral multiples of the frequency of a fundamental tone'.

So although one may hit the middle C key on a piano we actually hear the harmonics of that note way up into the stratosphere of khz.How high up? who knows?

Apols to the OP, sorry my posts are off your subject.
i have to agree with the guy who said MA BR is inferior to B&W 685's.. i've heard both and the 685's sound much fuller/musical
Gawdbless, yes there is a reason why tweeters can perform beyond the range of human hearing and that reason is called "marketing" ;)
Bob_Reynolds, thanks again for another interesting equipment suggestion, will research it in the near future. Regarding surround sound, I won't be able to place a system in the living room for about a decade - kids are too young. So I was thinking about starting to build up the speakers - B&W 600 series looks very nice.
I am going to stick with the 685s and definitely get a powered sub. Amp is TBD.
Thanks all...