Well, I should have never used two inches because that is what made you jump to conclusions.
To the OP. Here is the way I look at it. You know what you are capable of with your rifle at 200 yards and I will assume with what you can expect to find for a rest in hunting conditions. All things being equal you should be able to do about twice that at 400 yards. If your data is correct the charts are going to be very close to what is going to happen. That is why they made them. If at all possible shoot some at 400 yards somewhere so that you will be comfortable that is the case.
Like I said in my first post, the wind is what will get you. Keep an idea of what the wind is doing before you even see an elk and understand what it does to a bullet. Keep in mind that if you are shooting from timber across a gorge or something it may be doing something different out there. If you can't figure it out don't shoot. Hopefully it will be calm.
Once you get settled in to the best rest you can get see what your cross hairs are doing. Shouldn't take but a second. If they are wandering off all over the place don't shoot. If you can keep your cross hairs well within the size of the vital area of an elk your rifle will do it's part if you have figured the trajectory and wind correctly.
I'm sure they will pick this apart as well, but I have just never found killing elk with a good scoped rifle all that hard to do.