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
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" 
@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.
@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.
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.
15x20 is a good listening room. You can make pretty much anything work in there.  Sopra 2 Sopra 3 both would be fine. 
If your heart is set on Focal Sopra 2's they will work greeat in your room.  I have had smaller speakers in a larger room that you are talking about and they worked fine.  I assume you will be listening to them at 10-15 feet away.  Your bound to get tons of suggestions to consider other speakers.  I would stick to wha you enjoy.  Room treatments will help if your spouse will allow you to but SR HFT's also help.
I thought that would be a very easy way to flesh out your budget..........

Now don't make me beg for the amp/preamp and source you have or hope to have....
@OP,
I hate to be the stuck record, but have you considered Vandersteen?
IMHO, one of the best performance to price speakers out there.
If you can wait, a used pair of Treo's or Quatro's would be under $9K.
Bob
https://www.ebay.com/itm/Ampzilla-2000-Mono-Block-Amps-VMPS-626-Ribbon-Speakers-Trinaural-System-RAR...

<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>

Everything but the subs...

I heard a system exactly like this one with two "Larger subs" they have a 15"PR, a 12 and 15" active.

One of the best bang for the buck systems I ever heard.. This is a steal with amps, speakers and processor..

Pure analog, with bypass for pure stereo or the trinaural analog processor.. or a HT thing if that's your thing..

Regards
@sounds_real_audio

Suggested US Retail Price: $750,000/pair

if you're willing to make the difference from a $9500 speaker, sure!
@erik_squires 

room correction is on my radar.

considering a moon 600i v2

some pretty good deals here and on usaudiomart, as I could never consider this equipment new.
I think the Sopra 2 is a fine choice for your space.  Have you considered any room treatment though?

Also, these tend to be punishing for mediocre amps. Be sure the amp you plan on using is relatively stiff.

Best,

Erik