Assuming you're running on ultra at 1080p, it'd be normal for an HD 7850 to drop to ~45 fps in a few places outdoors. I remember looking at benchmarks for an HD 7870 in Skyrim, and at times even that fell to ~55 fps. Skyrim isn't that well optimized, really...
I found you can save performance without noticeably losing quality by using just 2x antialiasing + SMAA, rather than relying entirely on the in-game antialiasing.
Also, the item fade slider only affects tiny clutter objects like bottles and plates, so you can gain a few free fps without really losing quality if you put that at 50%.