well the 4-2-1 will be two piece, meaning the top part of the header which goes on the block will be seperate from the bottom piece that connects to the cat, and those two connect together.... the 4-1 is one piece, and for the 5th gens I know DC doesnt have one, not sure for the 4th gens.... as for the ceramic/stainless, it is basically all for looks, and some people seem to think the ceramic looks better, depends on what you want..... the 4-2-1 is better for lowend just because I dont think it will lose any, the 4-1 you sacrafice power down low for gains up top.......