B&W vs. Sonus Faber

As others have said, let your ears guide you. I know it's hard because you're listening to SF and BW in different systems. I own 803 D3s but am not intimately familiar with SF so I won't try to compare them. I used to run my 803s on a McIntosh but now on a Pass Labs power amp. I love the 803s. I've not heard the 802s (someone said they have a better mid range). The 803s are not too bright for me as a rule. I find that production values vary so widely from one recording to another that it's sometimes hard to generalize about a speaker when the production values are so different. I can say the 803s have plenty of bass and exceptional detail.  Depending on the amp, the speakers can disappear in the room, fill it entirely, and create a very rich sound that is almost liquidy. I'm sure SF owners will trumpet their speakers as they should. This is a +1 for B&W.  It's common to see used 803 D3's go for around $10,800.

Not sure buying used spkrs is a good idea.  No idea if they were abused and you’ll never have full confidence about what you have.  
Used cars ok, but speakers a lot tougher.

I’d much rather buy old speakers instead of used cars. As long as the speakers are less than 5-7 years old, there are fewer things that can go wrong. I’ve bought almost 7 pairs of speakers in the last 15 years, all used, zero issues. Knock on wood!

I agree. I don't see many people spending say 6 or 8 thousand dollars, if not more on high end speakers abusing them. Or any piece of high end audio equipment for that matter. I think most tend toward being obsessive about their gear. I know I am. 

 I would be far worried about  buying a used car.

B&W on the other hand will grab your attention immediately. Once you take them home, YMMV.

B&W D3 are a very revealing speaker and can be picky with components.  The amp/preamp can make or break this speaker as I have heard D3 sound like crap or sound boring but also sound totally amazing.

The Sonus Faber are going to be more forgiving on bad or flawed components, so they will likely sound more "pleasing" in a higher number of systems.  But they are not going to be as transparent or accurate in the high frequencies as the B&W diamond tweeters.