Greetings,
The 308 covers medium size game very nice. If you want another rifle, perhaps you should consider a varmint rifle, or a big boomer for fun at the range. However, it is much cheaper to shoot a 223, 22-250, 6mm, or a 6.5 mm than a 375 or 416, or 458 magnum. You can easily buy ten boxes of 223, for what one box of 458 magnum cost. And the 458 is a bit much, for bunnies and bushy tails that can be easily hunted close to home. I am very happy with the 6.5 Ruger Creedmoor. It can kill medium game with ease, works nicely as a varmint rifle, and with low cost lead bullets makes a fine small game cartridge. Get the most for your hard earned dollars.
Mike 8)