At what point does one cross the line (in longer distance shooting) in moving up the scope magnification ability? I have an S&B Classic 3-12X42 which I use on my 6.8 out to 500 yards without too much issue (considering that I have almost 70 year old eyes). I am in the process of acquiring some guns to shoot out to 1-1.5K - is that the point in time to up the magnification to something like a 5-25X56 power scope? Or is just a personal, "see what works for you" situation?