I have not seen any benchmark results with the integrated Radeon HD 7660D and Radeon HD 6670, but I am confident enough to say that at best it might be as powerful a a Radeon HD 6750. That is less powerful than the Radeon HD 7750 which is basically equal to the HD 6770. Additionally, I would assume the game needs to be able to take advantage of "Dual Graphics" / hybrid crossfire to get the combined performance.
In a nutshell, you are better off with the Radeon HD 7770.