The main reason accuracy starts to fall off is throat wear and tear. For those that don't know the throat is the section of barrel that transitions from open chamber passed the end of the neck to the rifling. As this becomes worn the rifling loses it original shape begins to crack. What causes this to happen is heat. So if you take a cartridge like this and shoot 1-3 rounds and let the barrel cool, it will last twice as long as if you are shooting 20 round strings. If you are going to be shooting this in rapid session I would recommend the heaviest barrel you can.
Most hunting rifles will never need a new barrel. The barrel life on this round is probably somewhere between 850-1500 rounds for top level accuracy. As NW80 pointed out, if you shoot 30 times a year it would take just short of 30 years to burn it out and that is the low end.
Now having said all that, anytime you can speed up those 6.5 bullets you are going to be happy. The effect range of a 260 is already much farther than most can/should shoot and if you add 300 FPS you can take even more wind drift and drop out of the picture!!
NW80, I would be happy to help you out with this build if you are lookin for a smith