I would rather drive the old Mack CH600 instead of the new Internationals for two reasons. The noise level, and the seat adjustment. Same here, my knees go numb, and no head room. The seats are horrible, as they do not adjust very well. We don't have any Sterlings here.
Forget that. I get about 6-7 hours a day driving in a new pkg car and the "new" seat feels like a book stuck under the seat cushion(lumbar). I was in a Mercedes van which felt oh so good. Summer camps force me into a P-570 and what a problem. It rides real rough MT and has no side (lateral support). Seat belt has no tension to hold you in either and there no shifter to lean on. I even offered to buy a air ride or springer with side support and UPS said "NOPE".
The low seat (12-14 back) in P10 was changed out for the new high back style seat. While the seat is slightly more comfortable. The mounting bracket is not an exact match. The seat has a slight rock to it. The seat rock backwards when stating up from stop and tilts forward when you are braking. Gives you that Dale Jarrett racing expreience all day.