You're transposed in your thinking
The Aspect/Cambria are Class B's (slimlined), Impulse/Access are traditional C's.
I have a '12 Itasca Impulse Silver, took delivery in May of this year. It's a Class C. We opted for the bunk over the cab instead of the entertainment center (have 2 youngins). . I liked them also but the difference is head room. The Impulse is 6' 10" in the living area and 6'4" in the rear bedroom, the Aspect was 6' 4" throughout I think. I'm 6'3" and needed a little bit of head room. Plenty of room for 4 of us and a 100 lb Goldie.
Hope that helps if you have any more questions let me know.