At this point of the play I would definitely say Macbeth is insane. Ever since the first meeting with the witches, he cannot get the idea of becoming a king out of his head. He began plotting against the actual king in order to kill him and has begun talking to himself. He goes on and on about the murder and how he will, if he were to, do it. Macbeth does have his moment of saneness when he says:

"He’s here in double trust:
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host,
Who should against his murderer shut the door,
Not bear the knife myself."

but yet completely goes against it his own reasoning's. He thinks too much about the issue at hand and doesn't know what to do.