Is there any legal restriction from flying above your certified service ceiling if you are actually able to? For example, turbo 182 has a certified service ceiling of 20K ft, but its climb performance is still rated for 725 fpm at 20K. So, it looks capable of higher. So, I am wondering that if I am IFR and about to cross some ice laden clouds where their tops are at FL 200, could I legally request say 21 to 23K if the plane will actually take me there?