My space is open and very similar to yours. At the widest it's 17 feet but mostly 14 ft x 40 ft long with the kitchen on the other end and furniture 12-15 ft away from the speakers. I listen mostly from the furniture, so my expectations may be different from yours. I'm relatively happy with my Paradigm Persona 3f speakers but would not mind the 5f or even larger. I do have 2 15 inch subwoofers, so they do add a lot to the whole effect. The 3fs are connected to a 400w Anthem amp. It certainly fills up the space with volume but not what people might think at low volumes.
My biggest issue might be the side wall reflections sitting that far away. I don't worry about rear walls because I sit about center of the space. I also have the speakers about 3 or 4 feet out from the front wall. Low volumes for me are not that great from my listening distance 12-15ft with those speakers. Hope that helps. Good luck.