This is interesting. I tried vanilla skyrim with the Official HD texture pack, all graphical settings turned to 'high, 4XAA, 16XAF, averaging out at about 8 on the scales for object/actor/light fade (specularity set to max). I basically rarely went over 25 fps, and in some places it dropped to about 12. In fact, it crashed, not too far into the cart scene (a bit further than usual) :\. The GPU-Z log says I was running at about 750mb of vram for the entire time, but don't think that's enough to cause a crash right? I don't think I've ever actually tried using the official HD pack, as hadn't really played Skyrim since they came out. Always thought my PC could handle it.
So I tried with plain old ugly vanilla skyrim with the same settings and my FPS was improved (averaging 25-30 although still a bit sluggish in the busy places i.e. approaching the town, getting my head chopped off, etc) but it didn't crash and Vram usage was about 640mb.
I'm pretty certain that it used to run better than that before, although I did download the latest beta drivers the other day.
Does this tell me (i.e. you) anything? I'll do some more testing tomorrow and get some proper notes.