Ok, give Kalibak a LOT (I mean tremendous amounts) of steroids + a lantern ring and poof. Terrax. :P
But seriously, Terrax is a legit planet buster who can hide within the event horizon of a black hole without harm. Old Sentry blocked his best energy blasts with one hand. Caught his axe casually then crushed it AND Terrax's hand all with a bored expression on his face.
Sentry has never fought Surfer. That fight would be pretty cool. Surfer could probably find ways to damage Bob but not put him down and out. Sentry's raw durability and soak probably keep him in the game enough to flood the area with energy flares potent enough to finish Surfer.
Sentry's a lot tougher than most base form modern Supermen, yeah. Unified Sentry is probably still floating around Thanos level tbh. Let's say he is like... 3x tougher than his old self. That's still not enough to suddenly bridge the hefty gap between the Thanos and Odin crowd. Just my opinion.