I bought my wife a 46" Element ELEFT466 HDTV (college girl was getting rid of it at a very cheap price, couldn't pass it up), and attempted to hook it up to my PC via HMDI. The display and the PC report that it is using 1080p, but the actual image is about half that resolution.
I have been using a Vizio 24" 1080p via HDMI as my PC monitor for a year or so, and I comparing the two, I am seeing about half the resolution (despite what the drivers, TV, etc. say) of the Vizio by the Element. Terrible image quality and all that too.
As far as I can tell, this is NOT an overscan issue. The entire screen is displayed (and I know how to adjust the scaling in CCC anyhow). This is a false resolution problem.
I've run through all the settings on the TV and Catalyst CC, but because they are (falsely) reporting the corrent resolution as 1080p, they aren't terribly helpful. (I did lower it to 720p, but that was almost unusable as the UI was grossly oversized.)
Have you checked in CC under "My Digital Flat-Panels" and then "Scaling Options (Digital Flat-Panel)", and setting the "Scaling Option" slider to 0% over scan? That's what I have to do on mine or it looks letter boxed (black borders on all 4 sides of image), setting that option to 0% makes windows cover the entire screen area.
Some 1080p televisions just end up looking like crap. Im in the same boat with a 27" Insignia 1080p tv connected to an AMD llano based computer. No amount of tweaking can really sharpen it up. The image is noisy, the color is off, and the contrast is poor. It's just a crap tv with crap internals, that has poor signal processing or poor shielding, or something. It's still passable for its intended purpose.
A spare monitor I have around confirms that it isn't the PC or the hdmi cable.