Cleverly was slightly hurt by that left hook against non-punching euro level fighter in his last fight. Got caught with about a 14 punch combination. And your telling me that Froch who hits fairly hard and accurately wouldn't spark Cleverly unless Clev has overnight developed into a genuine world class fighter? I would pick Froch lateish TKO. Whatever Nathan wants to do wouldn't work. If he tried to box then Froch would outbox him and if he wants to go on the inside with Carl then he gets brutally stopped. Nathan has no defence as it is, but especially on the inside his defence is terrible.
No, I wouldn't be completely 100% certain that Froch would KO Cleverly. Your argument for Froch destroying him is by looking back at a fight that Cleverly dominated and won in 4 rounds. The question was whether it would be a competitive fight. A late TKO for Froch would suggest that Cleverly would hang in there and make Froch work for the victory? Unless you think Cleverly would just stand there for 10 rounds and take a beating? Unlikely with his high work rate, fast combinations and how easy it is to find Froch. As I said earlier, there's big difference in age/experience. That doesn't automatically mean a one sided fight in favour of the experienced boxer. We don't know if Cleverly's chin will hold up against the elite fighters, it looks solid enough at the minute.
Cleverly still has to prove himself at world level, Froch has been fighting world class opponents for over 2 years now. Froch TKO10