IMO I think the best gun to kill hogs with is the Marlin 1895 45/70 you just know when the bullet leaves the barrel the hog will be dead when the bullet arrives. Why take a chance with a smaller cal?.
I'm going on my first boar hunt this year as well. Pretty much every seasoned boar guide/hunter told me the 45-70 will definitely drop 'em; that's their preferred caliber it seems. They do stress that, like 1tfl
said, its all in knowing the game and good shot placement...basic hunting 101.