In my experience, mail is worse than plate when it comes to perceived weight... with plate, the mass of the metal is distributed over the body; with mail, it's all hanging from your shoulders and belt*. Mail is also a fabulous insulator, especially with another layer over it. I've worn a steel haubergeon under a wool tunic and been ever-so-toasty warm, even in sub-freezing weather.
*Except that one time I forgot to pack a belt... Egad, were my shoulders sore...