100W, 200W, or 300W?

100 watts per channel could be enough but not that particular Mac. It sounds strained at higher volumes compared to other more robust 100 WPC amps.
200 WPC should be enough, I have heard that combination and it sounds excellent, the Mac takes the edge off the diamond tweeter nicely.
the 300 WPC amp would not be overkill but for your listening distance it will be more of a luxury / icing on an already very nice cake.
As a lesson more power is not completely about more volume. It is about sound quality and life-like dynamics and speed at lower volume too.  Think very good bass and attack at low levels.  The amp makes this happen.  
Some people like the jump factor dynamics in high efficiency speakers - you can get this with lower efficiency and higher power.
While the 7200 will be very nice, my ultimate recommendation would be a Mac tube preamp paired with their 200 WPC power amp. Boosts the spend but sounds like you have it, this would make your system golden.

Get the biggest best amps you can.
300W RMS, or larger.
 You need the headroom, said,many times, when crescendos, drum, or guitar solos, or the song ending slam at the end does happen, you will need the headroom.

I would agree with this statement.  I also have the B&W 805 D3 (previously had D2).  I tested two amps side-by-side with these speakers.  One set were 250 watt monoblocks and the second set was 500 watt monoblocks.  The were the same product line from the same exact manufacturer.  The 250 watt amps were nice, but if you listened closely, the smaller 250 watt did not have quite as much authority with bass (not quite as full bass and not quite as much slam).  It was almost splitting hairs, but the difference was there.  I think a 50-100 watt amp would sound even weaker (but it would still work). 

You don't buy big amps for the total power.  You buy them because they have huge power supply capacitance and transformers.  You will get a lot more punch, slam and midrange/midbass body.  The smaller amps with smaller transformers and capacitance just will not have the authority, EVEN AT LOWER VOLUMES.

The McIntosh sound is more of a mild and laid back signature.  If you say the autoformers create the McIntosh sound, it could be that the autoformers are responsible for the mild/laid-back sound.  Just a thought.  Not arguing against McIntosh.  It's entirely a personal preference.

Just food for thought.

Sensitivity Can be way over rated. I have 86 dB Vandersteen’s being driven by 40 watts of class a power. They will play loud enough to to shake the neighbors walls. Bottom line is watts per channel can become the main focus but you also have to consider the other aspects of the amp. If I had listened to all the threads I read on my amp and that it needed minimum 92 sensitivity I would have never bought the vandy’s. Everyone that has heard my system is more than satisfied if not impressed. I am very happy I rolled the dice and just went with my gut.

hi they recommend 50-120 watt amp@8 ohms that means thy don't have a power rating sensitivity 88Db @ 2' not 8' 8' will be about 82 Db if it had a power rating say 100 watts@ 8 ohms then your power amp should be 3Db higher will 200 watts @8 ohms remember the 805d-3 are good to 96Db spl and thd will be high

Thanks all:

In general it sounds like there is no significant danger by going big (just don’t crank the dial) - I’m more concerned with having enough headroom. Given the size of my room and the sitting distance, I have a feeling that I’ll blow my ear drums out or have the police visit before I blow the speakers.

@chilli42 Based on what I’m seeing Pass looks to be a bit more than I’d like to be spending right now!

@fbgbill thanks! I’ll likely take you up on that PM offer later on as I gather more info!

@twoleftears No one is pushing me in that direction, but it’s the combination of aesthetics and quality - I do understand that I can do better for the dollars but there’s always a trade to be done. The B&Ws fall in the same boat - can do better for the dollars - but they’re still really nice speakers and I really really like the way they look. Don’t want all looks and no bite, likewise, not after all bite and no looks - aiming for a sweet spot in the trade-offs! :)

@almarg that’s assuming you crank the dial, then you’ll likely blow the thing. I’m more interested in head room. Even if we assume that the speaker will blow after 120W, I’m concerned the 5300 will start to sound bad way before that because it’s pushed to the max. To use a car analogy, I’d rather be in a car with a 120 MPH top speed going 60 MPH than a car that’s rated for 60 MPH going 60 MPH... did it in high school, you’d think the thing was going to fall apart on the highway!

@avanti1960 yeah, I’m leaning towards the 7200/302 for those reasons. There is a case to be made for the 302 in that I can play around with different pre-amps afterwards to upgrade without having to change out everything. In the immediate term, I don’t even need a pre-amp... I can pipe my streamer directly into the amp.

@auxinput curious, what amps were those? What are you using now with your 805D3s?

@ditusa Yeah, that makes sense - with more distance, you’re going to need more DB. What would you recommend as a power range given the 805D3 specs? I’m currently giving it 100 wpc using a nothing-special amp (the Harman) and while it sounds really good, it feels like the speakers can be sounding much better. Don’t know how to verbalize it, but it feels like there is more to be had out of these speakers.