SMOS 1.3 is not very good for the older 7950's. You're better off with SMOS 1.0 with the older CGMiner 3.2.1.  SMOS 1.3 works better for the newer R9 series cards.  In fact a lot of the newer updates like Kalroth's CGMiner fork and SGMiner tend to like the newer R9 280 and 290 cards.  I'd stick with the ancient but working CGMiner versions for the 7950's.

I've got 4 MSI 7950's running between 680 and 710 on SMOS 1.0 with CGminer 3.2.1 using the undervolted .962 bios and Lantis' scrypt bin files:

http://i.imgur.com/rKiV8bu.jpg