They are the same to me. They imply that "he" is somewhat stubborn and someone should try to "talk some sense into him".

use speak for more formal presentations and lectures, and talk for more informal ones When we refer to languages, we use speak: How many languages do you speak? I wish I could speak Italian. Speak usually only focuses on the person who is producing the words He spoke about the importance of taking exercise and having a good diet. Talk focuses on a speaker and at least one listener, and can mean have a conversation I hope I can meet you to talk about my plans for the company. use speak on the telephone Who’s speaking?

I'd say in common usage, "speak to him" is a bit more formal while "talk to him" is very informal.

As far as I know both are same. but speak to him is more gentler, talk to him sounds little harsh.