The Boeing 787 has a design cabin altitude of 6,000 ft, the A350 is set even lower at 5,500 ft. The cabins are pressurized and maintain this level regardless of cruising altitude, be that 30,000 ft or 40,000 ft.

That's one reason (the other being increased humidity levels and the reduced noise footprint on those two aircraft) why they feel more 'comfy' to passengers.