Upgraded to the ultra from the arc. Biggest improvement has been dialogue clarity, which is very noticeably better than the arc, which used to fall down in this regard. The atmos performance is no better tbh. Of course, the standalone bass is much better with the ultra, but not really noticeably better than the arc when paired with the Sub 4. I’d recommend the ultra over the arc if ur buying into the Sonos system for the first time or if you’re upgrading, then if you can get £500 for your old arc and get a decent 15-20% discount off the new ultra, then it’s also worth the upgrade :)