I have been shooting and reloading competitively for over 20 years, from benchrest to 200 yds all the way out to 1000 yds. I have also been building rifles in that same time and they are all over the US. The number one thing to do to start is find you a Gunsmith/ Rifle builder that is very good and can put together a good combination of Barrel to Rifle and produce accuracy from the start. A Gunsmith that doesn't do the things required to be able to do this will only leave youvright where you started. The next thing is to educate yourself on ballistics and what makes some rounds more inherently accurate. When loading, keep in mind that speed isn't always better. I would rather tune a round down a few hundred feet per second if it meant making the bullet more accurate. A lot of people don't even consider sectional densities and Ballistic coefficients when choosing a bullet either. Very important. Consistency in the loaded rounds is also a biggie. Make sure everything is the same from round to round all the way down to case weight, bullet weight, charge weight. Make sure your bullets are seated to the same depth and are concentric. Not doing the little things will leave you frustrated. Education is the utmost important thing. If you don't know why your rounds are acting the way they are, you will never know what to do to correct it. I have found that bullets with the worst ballistic coefficient are the hardest to load and make consistent. You talk about the 6.5 PRC, well IMO the 6.5 has the best bullet ballistic Coefficient of any bullet, and I had a friend that was able to make dong hits with it in expiraments out to a mile and a half. That being said, I have also seen a .338 Lapua Ackley outperform one in 1000 yds. Pick your round, find a great Gunsmith, educate your self on loading for precision reloading and shooting, get quality components and powders. Even Primers can play a role. Lapua brass in my book are the best because the sort weighs, their all the same length, the internal and external flash holes are deburred. Just a very good brass. A little more expensive but you get what you pay for. When shooting ultra long range, a good ballistic calculator is a must. As is a good range finder. Remember your current weather conditions because they to play a part. I hope I didn't go too much into this subject, but I wanted you to see why it can be a little harder from one caliber to the next. Take care. I hope I gave you some info you didn't know.