6.5mm bullets are longer than the caliber suggests, so they like to buck the wind at long distances better than other calibers that don't have the Length/width ratio in their favor.
.257" bullets just don't have the Ballistic coefficients to keep up. BUT , that only matters a lick when the range you shoot at are 400+ yards. At the distances you like to shoot at, it really doesn't matter. Pick the gun that you can get the most cost effective ammo for. Check locally and make sure there is some of each. Then check the price, as you'll shoot the one you can afford to shoot more, then become a more lethal hunter because of it. (My personal preference is still .257" , as I LOVE MY .25-06 rem , and it has been responsible for me getting quite a few "timid" people to get the courage to actually pull the trigger) For 100-200 yard shooting, if you don't reload, just get the most practical round for you...............cheapest and easiest to find ammo. THEN MAKE FRIENDS WITH SOMEONE WHO RELOADS. It isn't rocket science, and once you are shown how, the sky is the limit. If a knuckle dragging moron like me can reload, then you could possibly win a Nobel prize doing it.