From tests people have done here (I don't think anyone has done a side by side), but just looking at the return times from different folks, there doesn't seem to be an appreciable difference in ms times between the GT1030 and P400. Both have got people from hundreds of ms down to sub 100ms in the 65ms range or so. The differences are probably more related to different fields of view and computer and setup than the card itself. It isn't until you get over 1,000 cuda cores that you can start to see the drastic improvements. But those cards are crazy expensive right now.