In my opinion, a student who recieves a C is not going to do much better if at all in Biochemistry. I believe that is a bad statement, because if the OP does take biochemistry and fails(on par with getting a C in Ochem would be a D or lower in Biochem right??) then that would make their transcript much less competitive.
If you firmly believe you can do well in biochemistry, which I would evaluate first, then take it. Dont take it to prove yourself over Ochem. Ochem is required, biochem is not. Its just like putting more money on the poker table, you might win, but its risky as hell!! 👎 I still think, just take it again, get an A, you already got a C, you know you can get a C, show improvement, instead of taking a class you have no idea about, and general concenus states its tougher than Ochem, IMO a stupid idea