I would buy something that gets some separation from the performance of the 06. The Hornady Light Mags and Federal High energy rounds have more KE energy than a 7mm Rem Mag and are only approx 100 FPS behind the Win Mag. That is why I would skip over the 7mm Rem mag and 300WM/300WSM and step up to a 300 Wby or 300 Ultra Mag. The problem however is that to shootaccurately at distances beyond the effective range of the 06, will require an awful lot of practice and that will be very expensive with those cartridges. You will almost need to reload or you will be broke by the time you are proficient enough.