It's (been) ten months since.....

Which of the following sentences is/are correct?

1) It's ten months since we have had that conversation.

2) It's ten months since we had that conversation.

3) It's been ten months since we have had that conversation.

4) It's been ten months since we had that conversation.

If all are possible, do they mean the same thing?

If so, which would use or do you prefer?

Thank you.