5.56 or 300 BLK for AR-15?

I recently decided to get a Smith and Wesson FPC, thinking that could be an adequate alternative to an AR-15 given its small footprint despite the 16" barrel. Upon further research, I've realized that a 9mm PCC simply won't do for SHTF situations in my red ass state.

An inconspicuous footprint in terms of storage is still a priority for me. I also intend to run with a suppressor, so that leads me to think 300 BLK would be right for me. Would something like the PSA 10.5" AR-15 Pistol in 300 BLK be appropriate in a balance of compactness, stopping power, and range?

Open to any other ideas.