The 357 Magnum will do fine within reasonable distances, and the GP100 is a fine platform for the cartridge. I load 16 grains of H110 behind a 158 JHP @ 1,500 fps. To say this bullet "worked" would be an understatement. You need to pick your shots carefully, but it will giterdun. You better have your ears on tho.
PS, $500 is a decent price, with the UltraDot.