I've ridden only in the back of current gen X5. I would say the seat comfort should be improved. It just feels too flat and upright. It is too stiff with no cushioning, and it doesn't really hug the body in. The bottom cushion should be tilted up a bit to support legs. And the backrest is just too.... I'll just say it feels like sitting on a bench. I hope it is reclined just a bit. And it should be shaped to come in contact comfortably with the passenger's back.
As for ride quality, I didn't really have a problem back there. I wouldn't say it is an overly comfy ride but it doesn't feel too harsh either. Feels much more spacious than ML, Range Rover, Cayenne, etc. back there as well.
2011 Range Rover Sport HSE with Fuji White and Ocean leather.
2011 E350 4MATIC with Calcite White and Chestnut Brown leather.
2013 650i xDrive cabriolet with Alpine White and Vermillion Red leather coming soon...
2011 328i Cabriolet with Alpine White with Coral Red leather
2007 ES350 with Tungsten Pearl with black leather