My Room Size for Speaker Consideration


As I look at possible speaker sizes for my new 2-channel, I'm wondering how I should look at my room dimensions.  The family room is 15' x 20'.  On the 15' length (where I sit), there is a knee wall that opens into the kitchen, which is another 10' x 20':

At it's smallest, it's 300 sq ft
At largest, it's 500. sq ft.

To better match the speaker size, which room size should I consider? 

(I'm dreaming of the Focal Sopra 2, and their website is kind to recommend room dimensions)
bgm1911
I have a Thiel CS3.7 in a 11 x 12 x 9 (plus extra room from closet). See my Virtual System photos. The room is treated with GIK acoustic panels and the digital streaming source is treated with DSP that was setup remotely by a super talented audio engineer. The sound is perfect and I even sit off center.

I have some links on some of my old posts that go into detail of how this was accomplished. Send me a DM if you want more details from me.
@yyzsantabarbara 

thanks for sharing info about those panels, they seem to be very popular as they're seen in a lot of pics and videos of systems.
@bgm1911 The GIK panels were nice when I had a small monitor in the room, KEF LS50. With that speaker the panels were all I needed. However, I wanted a bigger speaker in this space and the panels really do not solve that problem. They help but relying on those alone will not make a big speaker work in a small room.

If you are interested follow the links I listed on this post.
https://forum.audiogon.com/discussions/benchmark-la4-preamp/post?highlight=Mitch%2BBarnet&postid...

Take particular note of the article on AudiophileStyle.com web site. It is exactly what I also did. I do not even need panels to get to this level of quality but since I already had them they stayed put.
First I would not consider speakers that may be a difficult load. Now you are spending money on speakers which you may not like in your room ant them you are thinking it is the amplifier so you by some ridiculously high power amplifier and of course that doesn't help much you go with the room treatments advice... which will deaden the sound..... I mean there are a lot of system that I have heard at the RMAF that would sound better if they were turned off. 

As Art Dudley brilliantly says " if the first watt sounds like crap why would you want 200 more"