You aren't getting the point, ATI gets its shader count by multiplying the number of shaders by its possible instructions. So for the R600 you got 64*5 shading instructions = 320. Now if the rv770 has 800 shaders, you HAVE TO HAVE either 160 * 5 shading instructions or more shaders. No other possible way for it to happen, otherwise it wouldn't be "800" shaders.