There are a lot of variables in using a shotgun for home defense. I will state what my wife and I do, THAT WORKS FOR US; (which may or may not work for you). I am 61 and my wife is 62, in our situation the 12ga is just too much gun. Specifically, I had a rotator cuff repair and a total shoulder arthroplasty (replacement) of my shooting (left) shoulder in 09/2008. Bottom line is that my days of shooting a 12ga are gone forever. As for my wife, she shoots several 20ga guns well; but that is her limit of endurance. Many folks, so called experts, state that shooting anything less than a 12ga w/00 or 000 Buck; handicaps the shooter. (To which I politely state "HORSE MANURE"!) I have shot far too many deer w/small (2, 3, & 4 buck) to not be impressed with it's knock down power.
My life's experience has taught me that bird shot is for birds, buckshot is for bad guys. The longest possible shot in my home is 31 feet. I'm loading buckshot in my home defense shotguns, and not slugs.
We (the wife & I), use three shotguns for defense of ourselves within our residence...............
• Remington® SPR220 (Biakal® IZH-43) 20ga SxS loaded with Remington® 2¾"20 pellets of #3 Buckshot (#SP 20-3BK)
• Mossberg®500 20ga Pump loaded with Federal® Power-Shok® 3" 18 pellets of #2 Buckshot (#F207 2B)
• Ithaca® 16ga SxS loaded with Federal® Power-Shok® 2¾" 12 pellets of #1 Buckshot (F164 1B)
Federal® has a new 20ga load, #PD256; that has 24 pellets of #4 buck that I haven't tried but hope to as soon as it becomes available.
I'm sure a 12ga 2¾" 27 pellet load w/#4 Buckshot the OP asked about will do fine. (When I was a WA State Correction Officer in the 1990's it's the load we used and it performed superbly.)