To run the miner on all four cards you have to use -t 0,0,1,1,2,2,3,3. additionally you could add -a 1, which should be faster than -a 0 (which are the defaults) on  7970. There is no option "a".

what is the difference between using 0,1,2,3 or the way you mentioned?

thx

I have 6x 270x coming in soon and I was wondering what driver version/ windows would be best to have 6 of them running?