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
@sounds_real_audio

Suggested US Retail Price: $750,000/pair

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