On paper almost everything one writes comparing the 2 is probably going to go in favour of Utopia. But at the end of the day 800S to me sounds more natural & flowing. Utopia is extremely capable technically speaking.
The bass of Utopia is a touch more in quantity and a touch faster than 800S. A bass drum on the 800S sounds more like it is made of membrane; on Utopia it sounds more like a rigid surface (metal or something). Utopia also handles synth bass and electronic bass more confidently. Bass from brass and bowed strings feel more emotional from 800S. Guitar bass maybe Utopia has edge due to its nearness to the ear (yeah everything is near your ear on Utopia).
Impact means different things to different people. All notes on the Utopia hit you abruptly and leaves abruptly. There is not a sense of flow or sustain. And they feel like they originate very close to your ears. 800S feels like sounds originate a bit further and flows to you.
On 800S I feel Music is engaging. Same music on Utopia I m thinking of the prowess of the headphones- how resolving, fast and precise it is and suddenly I realise I ve missed half the track