Used vs. new

@OP. If your choice is between a D4 or D2/3 802, get a used one - they are more natural sounding than the D4 (within the overall context of those speakers generally having a distinctive house sound). Make sure an second hand pair is fully tested though as spares - tweeters in particular - can be difficult to get.

B&W : you may get better speakers for less.

B&W`s are known to be bright. You may need to spend more on your electronics to tame that bright sound, and have some amp power to drive them.

I own the 804N. Great bass. It puzzles me that others have claimed lack of bass in their B&W`s. 

I don't have experience with the B&W models mentioned here but owned 2 pairs of old B&W models for more than a decade, and I agree with few comments here that new is not always better. In my case, New and more expensive sound worse than old and cheaper. I owned the B&W CDM 1 SE close to 15 years. Midway through the ownership, I tried the more expensive model, N805. To my ears, the cheaper CDM 1SE sounds better than the N805. A matter of preference. I sold the N805 after about 3 months. 

Just to add. I will only buy used if the condition of the speakers is very good, perhaps 8.5 to 9 out of 10. I wouldn’t mind paying a bit more money for a good or mint condition pair. It’s good to have some savings if buying a used pair. The downside is most used speakers out there are in fair or poor condition, cosmetically, although functionally there may not be any issue. It’s the same with other hifi equipment such as amps or DACs etc.

If you are a meticulous person and cannot accept something that looks far from perfect ie. scratches on the cabinet or nicks etc., go for new.

New everything for me, unless of course vintage is your thing.