Antialiasing GTX 550Ti

Having followed Word Not Allowed's guide to the letter ( and I'm very grateful) I have greatly improved my FSX performance with one exception,there is terrible cockpit and foreground shimmering. I found that adjusting one line in nVidia Inspector and allowing it to enhance the application settings instead of overriding them improved the situation greatly but not entirely.

Why is it generally recommended to override FSX antiliasing? Certainly in my case (with an "average" GTX 550Ti card)_the results were not vey encouraging.