Is the royer a screen or just an aerator? Looking at the process I don't think it would take much of any thing over an inch or two. How fine are you looking to screen the material too? I will say with clay, its hard to screen through anything finer than a 3 or 4 inch screen. We use a read (metso) CV 150D fed by a 980 loader or 30 ton hoe, although smaller models are made. For clay we use fingers on the top deck and a 3 or 4 inch screen depending on dampness of material. If its wet at all, we don't even attempt clay. For our sod underlay we use a 1 inch screen in the lower deck and punchplates up top. We don't usually use anything finer than a 3/4 screen in it.