One factor, which you sometimes hear, is time. Scopes, and eyesight, deteriorate over time, My 30 year old Burris Fullfield, which sits atop my primary deer rifle, was a great scope. It still performs more than well enough for the hunting I do. Recently I've noticed it's not as clear as it used to be, but neither is my eyesight. And that scope has seen some hard use. I've not always been as careful as i should. So, all things considered, maybe it's time to update my glass. Not because the scope/rifle doesn't still shoot better than I can, but because the science of optics has come so far in the past 30 years. In evaluating optics, you can (I believe) come to a point where you have to be honest and ask whether you are capable of judging minute differences between scopes or whether the judgements are really mostly subjective. The only really objective questions are: Can I see and aim as far as I personally can shoot? Does the Point Of Impact stay the same?(There's a can of worms.) What can I afford? How much is the additional capability or "coolness" worth?