For a room of this size, my biggest concern is going to be the distance between the speakers and the wall behind them. Any rear-ported speaker is going to be problematic. Of all the speakers mentioned above, Harbeth P3esr will be my top recommendation. It is a sealed design and can be placed as close as 6 inches from the wall. In fact, when I had them in my home office I found that the bass response actually improved as I got closer to the wall. It really shines in near field listening, which let's face is what you're really talking about here. Although I sold mine last year, it is one speaker I won't mind buying again. It might not impress at first, but it definitely grows on you over time.
Having said that, if you can keep the speakers at least 18 inches out from the wall, the Fritz Carrera BE's are phenomenal speakers for the price. These are without a doubt my favorite bookshelf speakers under $5k. I'm auditioning a Rogers 65-v2 SET amp, and the combo is outstanding. This speaker really shines with tube amplification and can thrive with even low powered amps.
I also owned KEF LS50 (non meta version) and in my opinion they're not a great match for tubes. They really need some SS kick in the gut to wake them up. Same for Harbeth 30.1 -- awesome speakers if you pair them with beefy solid state amps, but quite ordinary when driven by tube amplification.
The smaller Proacs are also nice but I feel they might be too 'in your face' in a smaller room. I always found them to be a bit too 'lively' for my taste, but you never know. A lot of people love Proacs, so maybe it's a preference thing.