I thought there is no BIOS signature verification for Windows 7. That is just new feature for the Windows 10.

What is the speed when you mine the ETH only? Is that the same 27 MH/s or the 31 MH/s mentioned by the OP?

that does not sound right you should be getting at least 27-28 eth and 400 sia, the whole point of dual mining is to keep close to max ETH hash rate and mine SIA as a bonus

No.
- turn on the iGPU (set it to Auto if possible, so it's always disabled when you don't connect any monitors to it but enabled whenever you do)
- move your monitor to the iGPU (you might loose the signal on the discrete cards anyway and you might need to do this temporarily to stop the AMD driver from loading)
- have an AMD driver installed (doesn't matter if already "cracked" or stock but I will assume stock here)
- flash your cards with custom BIOS (if not already)
- reboot to Safe Mode to replace the DLL file with the cracked one (if not already)
- enable the Test Mode with bcdedit permanently for every regular boot (and keep it enabled indefinitely) and reboot
- sign your DLL file with the tool linked above (preferably while in Test Mode but with the driver NOT loaded, either due to signature problem or no cards connected, etc...)

My exact journey was like this:
- flashed the cards
- enabled Test Mode for regular boots
- rebooted to Safe More (note: not Test Mode yet) and applied the cracked DLL
- tried but failed to reboot into Test Mode (I ended up with a completely blank display, no life sign)
- moved the monitor to the iGPU and rebooted again into Test Mode (by default)
- I signed the cracked driver with the linked tool
- rebooted (yet again into Test Mode as always from now) and saw the AMD driver loaded
- I shut down Windows, move the monitor back to the discrete AMD card (for WattMan to work), booted (into Test Mode) and everything works

1. Ok, fixed.
2. https://bitcointalk.org/index.php?topic=1433925.msg15950514#msg15950514

and finally, use this tool (while booted into Test Mode which is now the default for every boot, so simply reboot from Safe Mode "normally" = into Test Mode now):
http://www.ngohq.com/?page=dseo
to locally self-sign the cracked DLL (since Test Mode requires a valid test signature!) -> copy-paste the line above when asked for the DLL file location
(Don't try to use the tool to enable Test Mode! Issue the bcdedit command above manually. This tool is for Windows 7, not >=8 but it can still sign anything anywhere...)