Here is my personal take.
A high quality 3-15×50, 3-18×50, 4-16×42,, 3-20×50, etc. will outshine a mediocre 5-25×50 all day, every day. 15-18x is plenty for shooting out to 800-1000, especially on deer/elk sized game. I have made shots on coyotes @ 1327 & 1365 on 16/17x. Just yesterday, we were shooting at 545, 752, 851, 921, 1181, 1251 with my 6CM that wears a TT315M. Plenty of scope to shoot a 2" 5 shot group @ 851. And not at all underpowered for the 1251 yard shots. Tracking and return to zero are VITAL! Reticles are all preference. I like fairly simple ones with .2-.5MIL subtensions but no "Christmas Trees". I also only shoot FFP scopes, as subtensions are always accurate, on any magnification you are set on. I would sacrifice a bit of extra weight for an exceptional scope all day long as well.
As for factory ammo, the one major thing that would limit longer range shots is consistency. They might shoot great at 100-200, factory loads sure seem to lack in the ES/SD category. I have seen "premium" ammo like Hornady Precision Hunter, Nosler Trophy Grade, and HSM Gold all have big swings in ES, up to 100+fps. Good hand loads should be in the single.digit to mid 20fps at most. Plus, you can tailor them to your exact specs and choice of bullet, powder, velocity, seating depth, etc. If you have a buddy willing to reload for you, take him up on it. Any good reloads should be able to surpass good factory loads.
I would be looking at a 200-215 bullet, around 2900-3000fps in the .300WM. Elk magic out to 1000+.
A good rangefinder is a must. Leica 1600B, G7 BR2, Sig Kilo 2400, etc. Couple that with a good wind meter (I like Kestrel) and lots of practice, you should be golden. Practice further than you plan to hunt (out to 1200), and even 800 will be easier.