I'm not sure. Do you think 16-18 FPS is slow? I don't know what spec your PC is so I can't tell.
I would be interested to know what FPS you get if you had a variety of textures which you randomly assign to the cubes. Also, what speed you'd get if you plonked all the untextured cubes into a single surface mesh and displayed that. You could view the scene from a high distance in order to rule out fill rate as a culprit, I guess (or have I completely misundertood the meaning of fill rate all this time? possibly :) ).
I would be interested to know what FPS you get if you had a variety of textures which you randomly assign to the cubes. Also, what speed you'd get if you plonked all the untextured cubes into a single surface mesh and displayed that. You could view the scene from a high distance in order to rule out fill rate as a culprit, I guess (or have I completely misundertood the meaning of fill rate all this time? possibly :) ).