Re: 270,270wsm,308,300wm
If you don't reload and you don't plan on hunting long range with the rifle than i would suggest the 6.5 Creedmoor. It has great barrel life, better performance than the 308, really accurate factory match ammo thats affordable, and if you want to get into reloading the recipe to copy the match ammo is not a secret. Hornaday has shared the information to copy its loads. If you want to shoot 1,000yds this cartridge is better suited to your needs.
If you are an experienced reloader and plan to hunt long range than i would suggest a number of different cartridges for 1,000yds. I am using the 270 WSM with a 9 twist Benchmark barrel. With the 170gr class bullets the performance is 3,000fps with a .700bc which is fantastic long range performance. The 7 WSM is perhaps a little better choice for long range since it has at least 8 bullets to choose from that are above the .600bc mark. If you are not recoil sensitive there are the bigger magnums like the 300 Win and 338 Lapua that offer bullets with really high BC's but for paper only i wouldn't suggest it as it is expensive to reload for.
270 bullets
165gr Matrix .650bc
169.5gr Wildcat .650+bc
175gr Matrix .700bc
Berger 170gr EOL .703bc
...plenty of bullets to choose from other than the Berger 150