I have the premier trim with 68b color accent group. its a nicer grade of leather. It also has leather on the top half of the door, surrounding the panel of leather that is stitched on all of the premium models.
The 68B is NO downgrade. And the 50th AP is basically the same interior, so they can be considered in the same breath. The seating surfaces are leather, period. The rest of the seats (premium and premier) are vinyl. The leather in the 68B is "top grain," a notch up, softer and more durable.
The door cards are different, with more and contrasting stitching. Th tops of the 68B doors are upholstered in something soft (leather? really good vinyl?) rather than being hard plastic. 68B also has color-contrast stitching in several places including the shift boot and the top of the console (gray on black, red on Redline).
There is a VERY long thread on this subject back in July, when we first discovered (Thanks to Tony Alonso) that the 68B was the ticket if you wanted the soft upper doors. HUGE discussion on that, eventually informed by Ford Service. 68B/50th AP is definitely the "top of the line" (except for the LE, which is the same in prettier colors) but the Premium and even Base interiors are all leaps and bounds better than last year, or anything Chevy ever put in a Camaro.