They probably are the same class.

The Class sizes really don't have much to do with a combines actually capacity.    I believe about all that is used to determine which Class a combine is, is the hp and grain tank size.

The 2377 and 2366 are going to be pretty close to each other in both of those comparisons.

Most cases in the real world a 77 will run circles around a 66, especially after a screwdriver turns the 77 into an 88.