[/quote]Having gone from fb1+'s to mb2s, and in a relatively small space, I would say you shouldn't be afraid to go further up the line than ob1's.
In my setup the speakers are about 2.5m apart and I'm sitting about the same distance away. Amp is 14B-C series. The sheer weight of sound, and the massive improvement in clarity in the midrange compared to the fb1's, make it a truly visceral and sometimes actually frightening experience.
I admit that it may look a bit silly having such large speakers in a small space, and I had expected complaints from the other half about this, but they never materialised. Can't say much more than that!

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From FB1 to MB2 is three steps up the scale! It is a massive improvement!
In my space speakers are abot 3m from each other and from my listening position.
I agree with you that a small space must not always be against big speakers.
Well positioned and with good room acoustics it is real joy!
Visceral impact is phenomenal, just like in big concerts!
System upgreded like this improves your listening experience but deteriorates your relationship with neighbours and can can be wife and kids unfriendly!
Luckily Bryston/PMC systems are just as good at low levels.
If you are lucky enough to live in a house (not in apartment block like myself) you are priviledged to enjoy your system all the way!