Welcome to PW, DickTracy! I will start by giving you the third degree!
So, are you committed to buying new?
Is there a reason you're only looking at Yamaha and Kawai so far?
How big is the room where the piano will go?
What are you playing now?
Where are you located? (If US, what region?)
Ok, having said (asked) all that... Yamaha and Kawai make very nice pianos. I am not fond of the Kawai action, but that is personal preference and not a statement about the quality of the pianos. Nevertheless, I don't recommend that you purchase one you haven't played (I mention that because of your comment about waiting for a piano to ship).
As to the size, those pianos are all reasonable sizes but where will the piano be placed?
I have a Yamaha C2 (5'8") in an approximately 11 x 18 foot room (there are two doorways as well, so that also plays a role in the sound). In any case, I could fit a C3 in here, but then I'd never be able to get around the back (tail) end of the piano, so for me and how this room is laid, the 5'8" size is perfect. And it sounds great, though that has to do with the placement in the room as much as the sizes of the piano and room.
Piano shopping and talking about piano shopping are some of my favorite things to do, but I'll stop here.