The most popular game bullet among 6.5mm fans is the 140 grain. It has a SD of .287, about the same as the 190 grain match bullets made for long range .30 caliber target rifles or the 160 grain 7mm bullets intended for deep penetration in heavy game. Typical reloads drive the 140 grain bullet at 2600-2800 fps. A good shot with a "puny" 6.5x55 Swede rifle loaded with 140 grain bullets can take most of the big game animals in North America.
If it is a herd of pachyderms that needs to be thinned, use the long 160 grain bullet. 160 grain RN solids (loaded in the somewhat smaller 6.5x54 Mannlicher cartridge) are what the famous British ivory hunter WDM Bell used to kill the many of the 1000 or so elephants he shot in East Africa. A 6.5mm 160 grain bullet has a SD of .328, about the same as the 220 grain .30 bullet (also used successfully on elephants) and greater than the SD of any other commonly encountered bullet except the 500 grain .45 caliber, which was designed specifically for killing elephants. So, you see, when I suggested the 160 grain 6.5mm bullet as the answer to a pachyderm problem I wasn't entirely kidding! Reloads for a modern 6.5x55 rifle can drive the 160 grain bullet at 2450-2500 fps for serious punch at woods ranges.