Forget about the .38 special. It's only good to practice with in a .357 mag gun. Speaking of a .357 mag, I've taken one doe with it. The caliber does have enough power to do the job if you can place the bullet in the heart and lung area. Keep the range under 20 yards for best results. The .44 cal is great on most any animal in North America. Dirty Harry liked it for a darn good reason.
the .500 S&W is over kill and really not nessesary. But I'd love to have one anyway. I'm a fool for big bores.
If you realy want something bigger go for the .480 Ruger. I haven't used one myself but I hear a lot of good stories about it.