Consider a 7 Mag shooting a .534 Hornady SPBT at a specific speed ( ie, not an average) of 3,100 fps and zeroed at 500 yards. That's a pretty fair long range load. Hornady's #4 book of charts says it will drop 17.1" at 600 yards. Then, at 3,000 fps (100 fps slower) the same bullet expects to drop 18.4" at 600 yards, a full 1.3" difference.
An ES of half that velocity difference (50 fps) would only cut the drop to something like 7/8"? If even if that estimation is off a half inch, it's certainly not enough to cause a miss on a 600 yd. p' dog! And all that calculating assumes zero wind and mirage to make aiming harder and assumes each bullet is cutting one hole groups out to infinity, none of which is likely in my world!
I think an accurate, reliable load with an ES of 50, varying only 25 fps from the middle speed, is a pretty good load in the real world.
Not perfect, but pretty good.
I don't mean this in a bad way but have you ever shot a load with an ES of 50 fps at 600 yards?? If you have, you did so with some bad calculations!
In your example, you zeroed the rifle at 500 yards and compared the 600 yard drop. In other words, you only have 100 yards of distance in which you are making your comparisons. Of course the difference in the two loads will be small in this small distance. What you should have done is zero them at 100 yards or 200 yards or 300 yards which is a more "real world" zero for most hunting rifles. If you would have done that, you would have seen more of a difference--something in the order of 5" to 7" depending on the bullet, bc, and conditions. That is the pure theoretical difference without the other factors that will be in your "real world" scenario. These other factors are group size, bullet stabilization (some bullets don't like being shot that extra 100 fps faster) and accuracy potential. Now consider the fact that you don't know which particular round you have grabbed from the old ammo box. Is it the slow one? Is it the fast one? Is it the one in the middle? You don't know! So supposing you play the wind, mirage, breath, heartbeat, and all the other "real world" things perfectly (which 99% of people aren't going to do on the first shot), you still have a 4" to 7" variation multiplied by two for the real world for a final group size discarding the accuracy issues at 18" to 14"!!! So, a load like that WOULD make you have a less than perfect shot an a deer's vitals at the very best! You could hit him in the brisket, the lungs, or the tuft of the backbone hair or miss him entirely!
Now for fun, let's throw in a little real world accuracy into the equation. Contrary to what I hear at the local range on a daily basis come deer season, NOT EVERY HUNTING GUN CAN PUT 5 SHOTS INTO A .1" OR .25" GROUP "ALL DAY LONG". At least mine won't anyway. The only gun I own that can do that is my 6ppc comp gun and it will only do that "all day long" if I steer the damn thing right. So we have "built in" vertical and horizontal error in our group to start that only adds to all the other stuff we've covered already! So now your guesstimated 7/8" difference at 600 yards becomes closer to "can't hit the broadside of the backside" at 600 yards. Do you see the error of thinking a high ES load will cut it for long range or even medium range?? I hope so. Please tell me there are not guys out there trying to shoot Bambi at 600 yards with guns and load that have ES's of 50 fps!!!! Screw the whales, save our poor deer!