Either the 6.5X55 or the .260 Rem are great cartridges for medium size game. If you will be using strictly factory loads then the .260 Rem might be the better choice. Both are lighter recoiling the the .270 Win and take medium game just as surely. Because of their mild recoil they are both extremely conducive to being shot accurately. With their " long for caliber" bullets in any thing from 140 to 160 grains they penetrate and kill all out of proportion to their diminutive size. I have even used the 120 grain Nosler Ballistic Tips with complete satisfaction on Whitetails, (which are neither big, nor particularly tough when hit correctly). With any tougher bullet starting with the 125 grain Nosler Partition and going up the .260 Rem becomes an acceptable cartridge for both bigger and tougher game. I believe you will find either cartridge a " keeper" .