Brooke please take a screenshot of your Graphics Detail menu settings and attach to a post. This will help others if they are experiencing the same or similar results. Next, I would do these 3 things and test again: 1) First place known to rob performance: check to insure that the environment map slider is set to "none". 2) Place a check in the box next to "disable clutter in flight" 3.) Reduce your max texture size, this is accessible from the "video settings" menu available only before you "go online" to start the arena portion of the game.
It's not a performance issue, as I get 60 fps flying around. (I'm using default settings except that I have slider set to none and disable shadows and reflection, as those are distracting to me.) Then, I screw around with the time of day while pointing my nose at or near the sun, changing the time of day from about 6:00 to 7:00 to 8:00 back and forth and in between while moving my nose around and weaving left and right, looking at the sun. After a while, the sun starts to look a little strange (too much bloom, too much glare off water), and then the game comes to a near halt. Most people would think it has crashed, but if I wait long enough, I see that I get about one frame every 30 seconds or 1 minute. It takes a while for me to get out of the game with alt-tab or ctrl-alt-del (have to wait a few minutes -- the first time it happened, I hard powered off my machine to get out of it).
If I restart the game and don't screw around with time of day in this way, it seems to work fine.
This happens in dx11, but it does not seem to happen in dx9 when I do the same testing.
I've switched to flying in dx9 figuring that dx11 on Windows 7 might not be as robust.