There is no doubt that would be the best. He may have nowhere to practice at 400 yards. But, the laws of physics are not going to change and if he is an excellent marksman at 200 yards he is an excellent marksman at 400 yards. Bullets don't just decide to take a detour.
The bullets WILL be affected by wind and gravity. A 180gr bullet out of a .308 moreso than many, due to lower initial velocity (more time to be affected).
If you have never shot at paper at ranges expected in the hunt, with the bullet and gun you'll be using, under field conditions, then you have no business shooting at a live animal with that rig at that range.