5 GPU windows mining rig, 1x rx 470 + 4 x 7970 1 GPU gives extremely low MH/s

Hi Guys,
I decided to update my mining rig with a RX470, because there was no driver for linux yet I decided to switch over to windows.
Now I got everything set up and running I find that one of the GPU's, is only giving 2.5 MH/s.
Before, on linux, it gave around 19MH/s
Any suggestions on what is going wrong here?

My setup:
4 x 7970
1 x RX 470

Thanks in forward!