"Speaking of/talking of" - similarities and differences

I was told that "speaking of" should refer to a previously mentioned subject and should trigger a change of the subject. For example:

• Are you going to chip in on a joint gift for Frank? He has a birthday tomorrow.
• Do I have to?
• You don’t have to if you don’t feel like doing so.
• Well, I feel like smoking now… but speaking of chipping in, I will chip in 10 dollars. (WRONG)

I was told that "speaking of chipping in" is not used correctly here because it continues the discussion of the previous subject. It would be OK if it started a new subject slightly related to the matter of chipping in. For example:

• Well, I feel like smoking now… but speaking of chipping in, who even made it up? Isn’t it just another useless concept?

Now I wonder what if I used "talking of chipping in"? Would it be OK to continue with the subject mentioned earlier in that case?

• Are you going to chip in on a joint gift for Frank? He has a birthday tomorrow.
• Do I have to?
• You don’t have to if you don’t feel like doing so.
• Well, I feel like smoking now… but TALKING of chipping in, I will chip in 10 dollars. (CORRECT? or WRONG?)