Flat shooting misses the point. You can calculate drop easy, wind drift is harder to compensate for. Anywhere past 300-400 yds, the heavier bullet will drift significantly less and eventually drop less. Closer, the difference in drop doesn't matter anywhere.
If you're hunting elk I'd err towards the 180gr. If you don't plan on shooting past 300 yards it frankly doesn't matter which you shoot as long as you shoot straight.