I just got my X7 M50i and I still have my ‘16 XC90 T6. I haven’t had it long but as others have already said, the X7 is an incredible car. It’s clearly next level compared to the XC90, it beats it in almost every metric.

Luxury - XC90 already has a great design that has aged well but the materials in the X7 are nicer. The alcantara headliner, the merino leather feels thicker and nicer. The X7 cabin is much quieter and the ride is more stable so going at 80mph feels like 50. When combined with a more solid feeling build, it just feels more like a cocoon and then adding the awe-inspiring B/Ws, it’s really your own private space. The XC90 tries to be that and does a decent job but clearly the X7 is better at it.

Part of luxury IMO is not feeling like the car is strained, movement is more effortless and my T6 is neither. While it’s fine for everyday duty, it’s clearly maxed out and with ppl or stuff in the car, you’ll feel the car straining. The x7 40i feels noticeably faster, never mind the M50i.

Space - x7 has a bit more space and a more usable 3rd row than the XC90. X7 is taller adding more the sense of airiness in the cabin and captains chairs really help with spacious feeling.

I can’t comment on X7 reliability but late model Volvos should be fine.

GLS is a longer car and I found it gave more cargo room and about the same in passenger space. The only thing I liked was the captains chairs fold flat. Otherwise the ride was too floaty for me but that’s personal preference and when comparably equipped, GLS seems to be more expensive by several 1000s.