I think your approach is a good one. Work your way out and familiarize yourself with your rifle. What works and what doesn't and what your rifle likes.

My M-308 scopes are designed specifically for for the 168 gr HPBT and I think that is why the reticule is limited to 800 yards, aside to the rifle design with a shorter than optimum barrel.

Both the 168 grain and 175grain bullets are the preferred rounds by snipers. I can certainly see where Irrifleman is coming deom with the heavier rounds for further out. The mass is needed to keep up the momentum and resist influence from atmospherics on the way to the target.