The Mark II is a much heavier car. And it has less horsepower. When the Mark II was new, FoMoCo declined to list its horsepower but everybody knew that the Mark II had the '56 Lincoln engine which was rated at 285 hp. SAE changed the way they rated engines beginning with the 1971 models. So, by today's measurements, the Continental Mark II probably has 200 or so horses.
Performance is, of course, a relative thing.
A 1956 Volkswagen would get to 60 in about 30 seconds. A '56 Corvette would get there in about 7 seconds. Today, the performance gap has narrowed a lot. Well, when I first drove one in late 1992, the interior looked too stark. They've since added some rosewood trim to warm things up a little but it still seems a little too clinical to me.