Harbeth 40.1 vs Sonus Faber Olympia III

I have had 40.1's in my room for the past two years.  I love them more than any other speaker I have heard.  But, yes, it's always personal preference.  I find them to be the most natural sounding speakers I have heard, but they are not dramatic in their presentation, so some folks might not like them.  They sound best with classical, jazz and acoustic based rock.  Loud rock with kick drums and heavy bass are not the best on the Harbeths, but still listenable.  
Also, contrary to what some will say, amplification choice is really important to get the most from them.  I love tubes, but now I am using a Lyngdorf TDAI-3400 with them and I believe this is the best I have heard these speakers sound.  200W/channel into 8 ohms is an adequate amount of power to provide the right amount of finesse and slam, at least in my experience.  My room is not as big as yours, just so you know.  I had them in a bigger room this summer and thought they sounded even better than they do in my regular listening room, so you should do well with them in your room.  
I'm sorry I cannot directly compare them to the Sonus Faber speakers you are considering, but I have heard SFs at my local dealer and found them to sound wonderful.  They are also gorgeous to look at, which I understand to be important to some folks.  I would just be careful about disqualifying a speaker purely based on its looks, however.  I personally find the 40.1's lovely to look at, especially without the grills.  
Enjoy the hunt, and best of luck in your decision.

What are the Harbeth 40.1 and 40.2 differences ?

Inna - From what I've read, the 40.2 is more efficient and has tighter bass vs. it's predecessor.   The 40.1 is known to have issues with a bass hump.   Personally, I've owned the 40.1's for approx. 5 years and I like the bass as it is.

I agree with Snackeyp with his characterization of the Harbeth M-40.1 sound.  

If I were to compare the SF Olympia III and Harbeth M-40.1's to cars, I'd say the SF is more of an exciting performance car, whereas the 40.1's are a comfortable, relaxing cruiser that smooths over the bumps in the road.  I only heard the SF Olympia III's briefly at a fellow audiophiles home.   I thought they sounded very good.   A lot of detail, fast and slightly dry/crisp.  Definitely a well crafted speaker and beautiful to look at, but I think I could tire of the detail and crispness of the highs.