B&W 800 D4's, Room size, & general Q's

Regarding B&W, it has been commented upon that their tweeter sounds very bright.  McIntosh tube products are considered by many to be very warm sounding.  I have heard them together, and those characteristics balanced each other out very nicely.

A brand of speaker not yet mentioned is Sonus faber which are unanimously considered to be Italian goddesses in the looks department.  They are fantastic sounding to me. Personally, looks are important in a speaker. 
These are generally comments.  Have fun!   

I have heard the 802D3 and 803D3 both on McIntosh amps (mc611). 
The 803D3 has no bass… for me me at least. It sounds thin. The 802D is better and with your budget I would be looking at the 800D, your room is fine. 
I have owned B&W in the passed and it really wore on my ears. I was happier when I moved on a long time ago. I really like McIntosh amps, though they are not popular on this site. I A/B a few amps and bought the MC462 which I am happy with. 
Once I had the Wilson Audio Sophia 3, 802D2 and Thiel 3.7 in the same room/ system for a back to back A/B with a few A/B of amps thrown in there too. Moved speakers around to their best spot for each one (awesome dealer!). That day the B&W held their own but it was easy to see they were colored once played back to back like that. B&W is very detailed but the frequency response is a rollercoaster. When you demo listen closely to the upper mids of the 800s and make sure you can live with it long term. 
The thing that stood out in this A/B was the dispersion pattern of each speaker and how it effected sound stage.

Rockport speakers paired with Boulder amps sounded excellent at the dealer. Good luck in your search ! 

100k is a lot. My system is closer to 50k and is pretty monster. Also, what you're going to get in a forum like this is a lot of what each person thinks is the best for that. I could rattle off my system and tell you it's great but it might not be your taste. For any amount of money, but particularly that much, I'd take the time to go listen to a lot of speakers and electronics. Keep an open mind to brands you're unfamiliar with. Maybe take a look at stereophile's recommended components over the past few years as well. 

I don't personally know anyone in DC/Virginia.  I would hope someone here could share if they have a great dealer they work with.  

I think you are very right conceptually looking at speakers first.  Find the speakers you like and then choose the electronics that you want to go with them.  

Here is a list of awesome brands worth taking a look at that sound different.  You initial thoughts of B&W, Kef and Focal is good.  They are big and safe and make awesome speakers.  

For a range of sounds, at least take a look at the website of the following brands.  Some of these look a bit different but all of these are speaker makers that make elite products.  

Wilson Benesch - carbon fiber cabinets handmade in the UK.  Incredibly detailed and fast.  I would look at the Vector and the ACT One Evolution.  These are a slightly forward but extremely detailed speaker that sounds massive.  Because of the relative neutrality, it works with a VERY broad list of amplifiers.  Everything from Chord and Ayre (a little brighter) to AVM and Naim (warmer) will work nicely.  Unfortunately, I think I am your nearest dealer just outside of NYC

Vivid - the designer here is one of the guys who helped make B&W great back in the 90s.  All are transmission line speakers made from fiberglass but sound incredible.  These are brighter like B&W, Focal and Kef and needs warmer amplification.  Bricasti, Naim, AVM, borg are all incredible with these.  I would look at the Kaya 45 and Giya G3.  Reach out to Todd through the Vivid website and he will get you the nearest dealer.  

Wilson - they are made from their proprietary materials which are different types of phenolic resin which is the material good PCBs are made from.  They are made in Utah and are brilliant.  I am not an expert on their line.  They are best with high current tube and SS gear.  Bricasti, AVM and VTL are wonderful options.  

Magico - Aluminum cabinets and wonderful parts make these speakers incredible.  They LOVE power and come to life with lots of headroom.  They are brighter and work best with warmer amplification.  I loved them with AVM amplification at NY Audio Show in 2018

YG - similar to magico.  Aluminum cabinets, etc...  They like power but don't need the massive reserves that Magico likes.  

Rockport - I would second looking at these and would not discourage anyone from considering them.  

Avantgarde - these are German horns.  Unusual looking and insanely revealing.  Careful matching is required but these are exciting and engaging speakers.  Look at the Uno and Duo.  Not sure who the dealer is in your area.  

MBL - These are omni-direction electrostats. Best with their amplification and the do generally need massive power reserves.  These deliver an immersive listening experience like no other speaker in the world.  

Raidho - These are ribbon based speakers that sound huge and deliver an incredible listening experience.  Not as immersive as the MBLs, it is sort of a middle ground between something like Vivid and MBL.  They have a lot of models that would work on your budget and work with a broad range of amplification.  I know their is a guy in Philly who sells these.  

Vienna Acoustics - These are a refined and well made speaker that is doing some really interesting stuff with drivers.  Strongly recommend them.  Reach out to Bluebird and they will put you in touch with the nearest dealer.  

Vandersteen - these are warmer speakers (best with Ayre).  Richard Vandersteen is certainly a legend in the US market and for good reason.  These are great speakers.  

If you review and research these, you will get a very good understanding of the range of options available to you.  I personally carry Wilson Benesch, Vivid, Avantgarde and Raidho.  The other products are just ones that you should consider if you are going to spend this kind of money.