Despero varies a bit wildly. Assuming top flight performances (Breakdowns, JLA/JSA) he is beyond any single person on the opposing team save for Thanos, and is in my mind an excellent match for the Titan. Assuming more middling level performances (JLA, Supergirl, Young Justice) his telepathy is incredibly powerful, enough that even the likes of Martian Manhunter, Superman and Hal Jordan succumb. As such he could potentially be a threat to anyone on the opposing team, but he physically would get manhandled by the likes of Thanos or even Sentry, I think. In his weaker showings (Superman/Batman) he was laughably ineffectual against Superman and went down to a single blast of heat vision. As such he would be beaten by anyone on the opposing team.
Assuming optimal versions of each, I'd say he and Thanos are a nice stalemate.
KC Superman against Silver Surfer is, in my mind, a decisive win for Superman. I generally give Silver Surfer about 6/10 against normal Superman thanks to a number of his trumps, but we are dealing with a more powerful, more experienced, more ruthless than ever Superman (evidenced by the JSA arc itself). He is essentially immune to kryptonite, has greater solar stores so energy absorption is going to be less of an issue and, again, he's stronger and faster than the original, who I view as stronger and faster than the Surfer.
Sodam Yat has yet to really prove himself in my mind. Lots of potential, but not a lot of skill. Luckily, the same can be said about the Sentry. I view Superboy Prime as more powerful than the Sentry -- decisively so -- and Sodam did decently against him, so I think he could probably stalemate Sentry for a good long while.
Eventually KC Supes helps him take down Sentry, and then they both help take down Thanos.
Not a stomp, actually a decent battle, but Surfer is the weak link.