I am purchasing a new scope for my 300 mag, which I would like to be 500 yard capable. Is a 3x9 or a scope to 10 power sufficient? Should I have parallex adjustment even at 9 or 10 power at that range? I am not looking to count ticks, but I do want to make an accurate shot and have a decent view of the target. Power costs money and I can buy a better scope with less power.