its all up to the shooter. but what will you be hunting the terrain and max distance is a good factor to consider. i find that if ur shooting minimal distance say out to 250yds that a 3-9 is perfect but with something larger u often think that you need to zoom in closer or get a better look at him. which can either bag your game or loose him.all you need is a good strong reliable scope that will magnify enough for you to place a good clean shot on your prey without counting the hairs on his back. lots of the hunters now days believe u you need a massive scope to do anykind of hunting with but that just isnt true, to be honest with u a 4x will pretty much do anything a 3-9 will but i wouldnt recomend it on varmint.i my self have lost a deer or two due to me trying to zoom my scope in and make uneeded sound and movement.your best option would to be to get a good 3-9 or say a 3-10 and mount it on that 308.