[Build Help] AMD Radeon 7970 vs 7850

My build is all ready and can support either card. The 7850 costs $260 while the 7970 is running for $590. My question is will the 7970 be worth the extra $330 in the long run? Or perhaps two 7850's down the road instead? I intend to use this as a gaming PC, not multi monitor or anything but want it to kick serious butt at least in the short term. Thanks for your help!