it seems to me that there should be no difference at about 100yrds between the bullets.
Au contraire.

When you guys pick the bullet for your gun, how do you do this? Are you going to shoot a lot of different factory ammo to figure out the bullet type and size and then develop a load to optimize it? Do you pre-select a bullet from your preference, usage (obviously will be a reason, hunting or target), what about the weight?
A lot of opinions on this but basically if your hunting you want the most energy possible. The heavier bullet flies slower but has a better BC and hits harder at long range. The lighter one can fly faster and flatter to a point, increased speed is energy on game. The 6.5's are so good with BC it comes down to range and purpose. The 140 class is really the best of both worlds. With 2850 easily achievable and long or extended long range accuracy being excellent why go any higher than the 143. But that's just me.