The simple answer: if you can swing the M3's $4200 price - I would go that route. You will definitely be covered on bass and not require a sub.
Change of plans.. for my 13x13 room, I moved my friends M3 Master into my house to see how a 32 Hz open baffle speaker would fare. Low and behold, the bass was MORE
. I guess 32 Hz - 40Hz box speakers I’m used to hearing don’t produce as low, accurate, authoritative, punchy bass as I thought they would (when compared to the M3 Master). We both agreed that no sub was required! Based on my earlier comment, I could see why you would want me to play it safe, but now that I’ve compared the two, we can put that worry to rest(?) The M3 Sapphire won’t be necessary. I’m not even sure I’d hear the difference because of how low the bass already is at my volume levels, so it might be overkill. But I will say - I’m drawn to the elegance and simplicity of the M5.
Great speakers, great price, great design!