ok the fastest Radeon is the x850 platinum-- it has a peak fill rate of about 8.64 Gigapixel/second. It can never exceed that..Your mistake is that you are calculating your fill rate by how many total pixels in each texture in each entity.. this is simply not how renders work. you rarely render all the possible pixels. Remember the textures are usually mipmapped or scaled down or up. The card ultimately renders pixels, but the engine internally doesnt think of that way.. it uses texels which arent exactly the same thing..no matter how big your textures are, you card has means of reducing the number of interpolated texels to draw to each pixel ( maybe i'm not describing this with scientific accuracy).. Whiles its true that a 2048*2048 texture scaled to actual size would take take longer to draw than a 128*128 tex scaled to the same size, rarely is a texture ever actually drawn to size.. usually its smaller, or larger, and in many cases when its larger it's not fully on the screen.. and often its shown through several mip maps anyway.

The point is this, its not as simple as you make it out to be, and your tests are flawed because of that.. no card will perform much over the listed peak rates... usually it will be under that for other reasons.

And to be honest, this seems to be a silly thing to investigate, as it has little bearing on what you do, unless you are really trying to optimize a multipass shader or some such.