Here's a concrete example:
My old speakers, North Creek Eska's, were a slender MTM mini tower designed for near wall placement small to medium rooms. They were housed in 13x13x9h room, open on two sides, and worked very well.
I've moved, and the room is 14x20x8.5h, pretty open on two sides; the Eskas, lovely as they are, pretty clearly lacked presence in this space. I replaced them with some fairly large (150 lbs, 53"h, 2 8" woofs) Montana EPS2s, which work very well. In fact, I think the room could handle larger speakers that move more air.
So based on my experience, the OPs room, of pretty similar size to mine, counts as a medium room that does not limit him to small speakers (depending of course on factors like the desired distance from boundaries.
YMMV, of course. Interesting that there are divergent strongly held opinions on this issue.
John