The 7970 is better. But you are comparing it with a Mac edition 7950. The performance is the same, but the BIOS on it is different. Mac cards are overpriced.
If you are choosing between those two, the 7970 offers the best performance. Or if you want to save some money, the 7950 is still more than enough to play at 1080p and can be overclocked to the 7970's performance.