I have the following settings on my 2xGigabyte 7950s setup (I got a couple of cards n the shop):
./vertminer -o startum+tcp://stratum.vertco.in:8080 -u -p x -I 13 --thread-concurrency 14777 --gpu-engine 1050 --gpu-memclock 1500
these are the best settings I can get without getting HW errors and all I get is a whopping
327 mhs 
!!!!
Apparently everyone has r9 280x now, so I have been having a lot of trouble trying to get better settings around here

Would be awesome if more people published their configs for 7950s
Cheers!

That's not bad. Remember hashrate is half of normal scrypt. Going to try your settings as mine (posted some 20 updates ago) got me a good 250Khs on HD7950's.