You dick, you know I lost my codices, lol.
That said, Carnifexen are known to be incredibly durable, I'm honestly not sure Dante can hurt it. They can also regenerate rapidly, depending on the fex, not sure if you're allowing a regenfex.
Carnifex are known for things like smashing clear through fortifications, ripping apart the adamantium hulls of tanks, toppling wraithbone spires, and shrugging off small arms fire. The 5th ed codex specifically mentions a carnifex surviving on a planet that had been subject to exterminatus and was rapidly healing in a hybernative state. They dropped a cyclonic torpedo on it.
I'd love for this Carnifex to have been Old One Eye. But alas and such.
According to Lexicanum, the any vehicle less than a super heavy tank has no chance whatsoever of surviving a Carnifex's charge. And even those fare poorly. That bodes well for it's strength.
As for smarts? Dante may finally be up against an opponent with less wit than himself. Without the guidance of the hive mind a Carnifex basically turns into a PMSing godzilla and just goes around breaking shit until it's hungry, then it breaks shit so it can eat it. haermm
As for durability? Well, according to Lexicanum, Scout Sergeant Tellion of the Ultramarines could -not- pierce Old One Eye's hide, OOE is a Carnifex. It doesn't state how Tellion attempted it on Lexicanum, but it does say OOE tore apart Tellion's squad, meaning he was probably pretty close. He was probably being shot at and stabbed/slashed at all at once. The only thing that saved Tellion himself is pulling a very lucky shot into the one wound on Old One Eye that had never healed, his lost eye.
IE... Not sure Dante can hurt a Carnifex, since Tellion had to shoot one where it was already wounded.
I vote the Carnifex smashes things until Dante gets tired, and then smashes him, too. The fact it has a venom cannon bodes well, too. Dante's cocky, swatting bullets out of the air and such. Trying that with the projectile from one of these will get him smeared across three provinces. >=D