As long as the internal dimensions and flow characteristics are the same for both the ceramic header and the stainless steel header, you shouldn't see any huge gains between the two. However, ceramic is more frail than steel, so under prolonged exposure to high temperatures and flexing from the engine, they can crack over time. The same is true for steel, but since it is a much stronger material, it should last longer, as long as it was well constructed. Also, like someone previously stated, you can wrap the headers to keep the excess heat out of your engine bay. This also helps to accelerate the gases out of the tubes faster, due to the properties of heat and thermodynamics that I won't bore you with. To sum it up, as long as the header was well constructed, a steel design is going to last longer than a ceramic one.