...there is no definitive answer to your question, because it depends on too many factors, with the size and shape of the room playing a huge role. And since everyone's room is different (especially the furnishings), there is no one proper action to follow.
Winston,
Realize you are tired of your B&Ws, but before moving forward on replacing them, in case you have not done so:
Have you tried (temporarily) moving the B&Ws into one of the arrangements suggested?
If they are setup 5ft from each other, against the wall, and you are 12 feet from them, perhaps you have not mined their full potential. Mind you, I respect B&W, but their speakers don't do it for me. So not making this recommendation out of love for them.
If you have not done so, then I see this exercise accomplishing at least two things:
That is, an eval on the B&Ws set-up in a proper triangle to you and at proper ear level, and within the room.
- if you still find them 'tiring' after you have played around with some placement options, you've checked off the speakers in a more complete way.
- if they surprise you, you've gained two insights, one that your speakers are better than you thought, and that rearranging the room to maximize your SQ may be worth making some adjustments to your current setup.
- David.