Trying to understand B&W’s trickle down strategy

800 series floor: solid milled decoupled aluminum 
tube loaded diamond tweeter all models.
Solid milled decoupled aluminum turbine head on 800,802, 803 D3's
Decoupled Continum mid range driver: Matrix cabinet construction for bass speakers: Aerofoil designed bass design with a woven fabric proprietary material: 
804 do not have the turbine head and the 805 have single continuum driver.
700 series trickle down from 800's: 702 & 705 Have the solid milled aluminum tweeter tube. 702,703, 704 Floor standers have the decoupled continum midrange but no turbine head models & they use aerofoil designed bass drivers but cheaper material than what is used in the 800 series & no matrix construction: The 700 series tweeter is a decoupled design with an aluminum tweeter that is treated with fine layer of carbon: hence: the carbon tweeter to extend the breakup frequency & to smooth out the performance over the standard aluminum tweeter. 
The 600 series shares the continuum driver material & the B&W design team so there is continuity to the house sound when you travel up the line. It uses a decoupled aluminum tweeter minus the carbon tweeter & traditional bass drivers: The 700 series has a more solid cabinet construction & higher end furniture grade finishes with superior magnets in the drivers.
Hope this helps; I have been selling B&W for 10 years & have attended a number of their training events over the years.

You will really need to listen with your own ears to feel the difference. I manage to sit in front of the 600, 700 and the 800 series playing with the same song, amp & room. I can really hear the difference between each of them especially between the 600 and 700. Of course you also need to note the life span as well since the matrix is an older system. Best of luck! 

The Matrix 805 in question here has held its value incredibly well. I have two sets. 
I think you should buy a pair between 550 and 750 if possible. Bring them with you to A-B against the new model you want to compare them to. If you are polite, ask for a time they aren’t busy, a shop of good quality should allow this. Then you can decide with some reasonable expectation of getting it right which you prefer. They may not be beautiful, and WAF not where newer ones are, but the SQ is (IMHO) extraordinary. 
I have a set of M804 as well, m802S2 as well. 
The M805 really punch well above their weight. 

The 800 series not only has the internal bracing and baffling to control resonances, but the drivers have bigger magnets with longer, matching voice coils. 

I've got 30+yr old Matrix 801-S2's that I've tried to replace with many newer speakers, only to sell those and go back to the old 801's.  There's simply something just "right" about them that I love, and the low end works really well in my room.  Some of the newer speakers had better resolution, or better dynamics, but none sounded as satisfying and simply disappear like my Matrix 801's.  I had Nautilus 803's for over a year, and loved the resolution, but they were a tad too bright & thin tonally.  I liked them, but didn't love them.  If you can find a nice used pair of 805's, try them!  You can always resell them at a minimal loss.