I have a 4 GTX 1070 and 1 GTX 1060 Rig hashing at 148 MH/sec, each GTX 1070 hashing at 31.5 MH that means an increase of 5 MH per GPU, I can help you to do that without modify the bios. I can send a print screen of my rig showing the hashrate....
I have done BIOS modification before with AMD cards, but it is a very risky task... how about if we start with the overclocking of the NVDIA cards without BIOS modification and then if you are satisfied we can do another job for the AMD cards?