Let's compare the cartridges you have listed. First the 7mm-08 and the 308, the 7mm will be slightly flatter but hardly noticeable, it's a 308 case necked down to 7mm. The 260 and 6.5x55 are just about the same thing with a slight edge to the 6.5x55. Having a flatter trajectory is not necessarily more accurate. For game up to elk any of the four listed will do what's asked of them. For factory ammo availabillity I would go with the 308 or 7mm-08, the 260 is becoming more popular but not readily available, the 6.5x55 is way underloaded in American factory offerings.