I having same issue. The graphics look like DOOM2 and my eyes hurts.. So you are not alone.
I also tried same manipultaions and have no effect. Static picture looks pretty fine, but when I move - picture becomes very terrible like DOOM2.
I am sorry but I am really enjoying this moment when I realize that I am not the one idiot with same problems ahaha
P.S. xbox360 phat white, HDMI <-> HDMI, samsung syncmaster p2470lhd. 1080p & 720p - no effect. Dont know what to do.
P.P.S. Update: and here we go http://gtaforums.com/topic/594659-getting-a-terrible-resolution/page-12