How large is your GT? How long before you have that 125gal set up and running?
People are trying to help you here, so pay attention to what they are saying. If you are impatient and just have to buy a fish, then why even ask? The point is, adding another cichlid to your 40gal could have detrimental consequences. You may end up throwing that money down the drain because either it or both of them will be killed.
It says in your sig that you have two 40gal tanks. Why not get what cichlids you want, and put them in the other 40gal to grow them out, and leave the GT alone in its tank. Then when the 125gal is ready, move them all over together.