Yeah, not sure I'm willing to sacrifice the shadow quality unless I absolutely have to. I ran an earlier version of STEP with everything on Ultra and didn't have too many problems, so with enough tweaking I can probably get it there again. I seem to recall RCRN's FXAA implementation being very good as well as cheap, so I might turn off the regular MSAA and do that.
And it looks like Whiterun is about 1050 and Windhelm is around 1100, which seems fairly normal for Ultra settings with the HD DLC. I'm running a GTX 580 with 1.5gb of VRAM and am allowing Skyrim to use 4gb of system RAM via the .ini so as long as I can keep it around 1500-1600 I don't think I should have much stutter.
EDIT - After comparing some screenshots of optimized SkyrimHD 2k and 1k textures, there's almost no discernible quality difference between the two. The 2k textures are a tiny bit sharper in some places, but not really enough to be noticeable while doing anything other than comparing still screenshots. Also, the new DDSOpt prerelease is amazing, it lowered the total texture size of the 1k set by 177mb.