You will need to do some bios modding on those gpu's.

ETH mining is heavly VRAM intensive. That means that you need to overclock the gpu memory as high as possible and use custom timings. In order to decrease power consuption, you should also underclock and undervolt the GPU core speed.

With 4 gpu's you should have something near 120MHs

Check the last pages of this topic https://bitcointalk.org/index.php?topic=1758267.0 and also search the forum for more on this subject