AA shimmering and "crawling" textures can really wreck game realism. I used to have 2 settings I'd use depending on what I was doing. I'd have high resolution with lower quality (no AA, etc) for dueling and scenarios where living was important, and lower resolution with all the quality sliders turned up as high as I could get without losing framerate. And I'd try to keep framerates pegged around 60 (monitor refresh rate), dipping no lower than 45 when things got busy, because framerate stuttering drives me crazy, wrecks any game for me.
Bottom line is if you really need framerate and high in-game performance, I'd recommend flying at a high resolution with the eye candy turned off and framerates pegged at your monitor's native refresh rate. If you are flying for fun, then turn the image quality sliders waaaay up and then turn down the resolution until the framerate is "fast enough" for you, meaning that framerate stuttering doesn't bug you.
In any case, if you're not happy with the image quality then throw more money at the problem. Buy an NVidia GTX980 Ti (or two), an obscenely high resolution monitor with 120hz refresh rate, and crank all the sliders up to 11. If that still doesn't work, sell the computer and get into RC flying
Edit - you TOTALLY need to check out this thread if you really want to maximize flightsim image quality:
http://bbs.hitechcreations.com/smf/index.php/topic,376467.0.htmlThe monitor tech they're talking about changes the monitor's refresh rate to match the video card's framerate output. This makes ALL games feel much smoother with far less image stuttering and tearing. But the monitor has to match the video card, so they're expensive. If I was single and still into gaming like I used to be, one of these monitors would already be on order or on my desk.