Can a car attribute be higher than the "maximum"?

It is possible for vehicles to have similar displays for their stats in the garage, but actually have different top speeds. In this case, that would mean that one (or both) vehicle's speeds exceed the maximum display in the garage. If you participate in a race on a straight track in GTA Online you will see that the vehicles do not have the same speeds. As you noted, the Massacro will slightly beat out the Jester in a straight line.

This is verified in this gamefaqs forum post

In my experience though, the handling of the Jester more than makes up the difference in speed that it lacks. According to the wikia articles for the Massacro and Jester there is less than 1MPH difference in their comparative top speeds. There are far fewer straight-line drag-type races in GTA Online than there are tumultuous races on uneven terrain. In most cases, handling will beat out top speed.