I had my latest built for a purpose; to shoot long range marmots. A half mile was the first goal, 880 yards. That was exceeded and extended to over 1100, twice, on the first outing. There was a lot of shooting all summer before that first shot was ever fired at a live varmint, to get from nice little groups to the ability to make those first round hits. Fine tuning of my ballistic software came down to an adjustment of 10 fps.
I have now extended the goal to 3/4 mile, 1320 yards. Shooting last Saturday in a gusty and shifting 5 mph wind was pretty difficult to get closer that 1 MOA, until there was a lull, and a carefully squeezed shot landed on the left edge of a baseball sized rock at the 1380 yard mark. I may be discovering the capability of 180 gr. Berger VLD's in a 7 Rem Mag.
Sounds to me like there is a lot of research for you to do yet!
I will agree though, now that I have this rifle tuned and have exceeded the original goal, I am already thinking of the next one. That one is looking like a titanium action, Remington Sendero contour, HS precision stock, or perhaps a McMillan of some sort using the Edge technology.
A rifle that weighs no more than 10 lbs scoped, capable of 1K yard marmot accuracy, should make a good LR hunting rifle that is not too much to carry around.
First, I need to finish fine tuning an 8lb, scoped, 270 WSM and move it past the 600 yard mark I have been shooting at.... and I picked up this 454 Casull a couple weeks ago that I want to hunt elk with. That beast is going to take some work to master. I have this 22-250 that is going to need a barrel soon... something suitable to make a better longrange prairie dog gun than the current 14 twist is capable of.....