I was thinking about getting a Glock 21 to replace my Glock 30 as my primary carry piece, but I think I'll just get a 15-round Glock 21 mag in September and just carry that as my second mag, for a total of 26 rounds of .45ACP on my person instead of 21.
I decided to always carry a spare mag after a friend told me her tale of four young toughs who approached her after driving past three times shouting lewdness, and her "oh crap" moment when she remembered she only had one 14-round magazine, having left her spare at home.
Predators travel in packs.
Fortunately they figured out what she was doing when she unzipped her Galco fanny pack and went to draw, and they all immediately jumped back in the car and ran.
I carry a Kimber Eclipse Target II, with a 10-round mag, plus I carry a spare mag; both mags with 165gr Corbon HPs.
14 rounds should have easily been enough for 4 punks.