If the TS you contemplate paying for OOP is not a Signature, then it is probably better to use the 2 credits for CRT and pay OOP for the remaining dinner. But if you were to go to a signature and pay OOP, you could easily spend more money than you would paying OOP at CRT.
In sum:
CRT on credits + regular TS OOP is cheaper than CRT OOP + regular TS on credit.
CRT on credits + Signature TS OOP is more expensive than CRT OOP + Signature TS on credits.
Again, all of this depends on what, and how much you order. You can get out of a Signature for just the price of a $32 entree if that is all you order. But if you do an app, an entree and a dessert at a Signature, you are looking at $10+$35 (or more)+$8 (on average) for over $50 pp before tax and tip.