Out of curiosity, why the flattest? Dialing elevation or holding over with a decent reticle solves the gravity problem. Wind on the other hand, IMO, is the challenge. High BC’s on the bullets for whatever cartridge you choose would be where I would be looking for 500 yard shots. That’s a game changer. Especially if (when) you decide to push a lot farther than that.
BTW - I’m a big .257 Weatherby fan, even though I haven’t owned or shot one in almost 10 years. Before rangefinders that was my go to.
