The element of the Kinetic energy formula that is fixed is the bullet weight so the more mass the bullet has the less it depends on speed to retain the power to do damage to the animal. In addition the Ballistic coefficient is usually better in a 180 than in a 150 grain bullet in 30 caliber so physics favors the heavier projectile at all ranges.
In more practical terms heavy bullets pushed pretty hard knock the heck out of stuff and give you greater margin for error. I use a 300 Weatherby to push 180 grain TTSX bullets fast so I get the best performance at longer ranges on elk but they work well at close range too. No substitute for hitting the vitals but use the heaviest bullet that shoots well is almost always good advice.
