If you want a competition rifle you're going to have to decide which discipline you want to compete in. A long range target rifle could be designed for prone or F Class shooting OR long range benchrest. The rules for these disciplines are not the same, so a rifle for either would have to be custom made or bought used.
Flexibility is not one of the things that is looked for in a competition rifle. Usually the bullet weights used in any competitive discipline is fairly well settled because those used work best. Cartridges range from various 6 mm wildcats to various .30 cal magnums depending on the discipline and class being shot.
The only mass produced rifles I know of that are suitable for long range prone or F Class shooting are the new Savage target rifles.
For short range BR there are no factory made rifles that will compete without more work and expense than a custom made rifle would take or cost to achieve similar results. The most popular and successful short range, 100 to 300 yard, BR is the 6 mm PPC for group shooting. Hunter (score) BR is mostly shot with .30 cal wildcats that have case capacity close to the minimum which is the same as the .30-30.
If there is a club near you that holds "factory class" BR matches go to a match to see what is being shot there. The club I was a member of in Seattle shot a factory class at 200 and 300 yards. Most people used .223's, with larger cases or larger calibers, when they showed up, generally didn't win except for the guys who could handle the recoil of a .308 Win for 40 rounds plus sighters from the bench. Not as easy as it sounds.
