The stopping power of the 40 is equivalent if not better than the 45.

45 auto
Load vel. energy penetr F.Dia. One-stop
230gr Hyd-shok 850 349 12 0.78 94%
230gr Goldsabr 875 391 14 0.75 93%
Corbon 185grJHP 1150 544 11.3 0.70 92%

.40 auto
Corbon135gJHP 1300 507 9.8 0.56 96%
Fedrl 155grJHP 1140 448 12 0.65 94%
165gr Goldsabr 1150 485 12 0.68 94%

.357magnum
Fedrl 125grJHP 1450 584 12 0.65 96%
Fedrl 110grJHP 1295 410 10 0.40 90%
125gr GoldSabr 1220 413 13 0.60 84%

Obviously, the .40 has consistently high stopping power. The .45 is roughly equivalent. The .357magnum, mostly a revolver caliber, has exceptionally good stopping power with an inexpensive Federal 125 grain jacketed hollow point.

Secondary defense calibers, with lesser but still effective stopping power, are the 9mm and the .38 Special. In both calibers, the most effective load is the Cor-bon 115 grain JHP+P. Both of these calibers, especially the .38sp, are known to have limited ability to penetrate intervening obstacles like automobile windshields, or hard targets like the human skull.

Load vel. energy pentr. F.Dia. One-stop
9mm auto
Corbon115grJHP+P 1350 466 14 0.55 91%
Rem.124grGoldSabr+P 1180 384 12 0.65 83%
Win 115grSiltip 1225 383 8 0.72 83%

.38special
Corbon115gr JHP+P 1250 399 15 0.58 83%
Win158grSWCHP+P 890 278 15 0.62 78%
Fedrl 125grJHP+P 945 248 12 0.69 73%

Corbon 115grain Jacketed Hollowpoints +P(highpower) are the clear winner...but these hot loads are expensive and should only be used in high-quality guns that specifically say they are suitable for +P ammo.

http://www.alpharubicon.com/leo/calloadgoshin.htm

Personally, I like 9mm, 45, 40, 357 and 38 special.

I just want the bullet to be in the .380 inch range or larger.