for the xfx cards, I dont know, I havent tried with those. try setting -5mv to start and see if that sticks. For the other question, yes it is worth it, but if you've never done it before I highly suggest only doing it on a card that has a dual bios switch (like the sapphire nitro). there are many guides out there, in my previous comments I put a simple step solution to get it working. but bricking cards is real, hence the dual bios switch. and yeah its better to dual mine, but it uses much more electricity.
Thanks Fr4nkthetank... I can confirm that dual mining does not use any more electricity. Tested with a meter at the wall and both readings are the same at 570w. So I have decided to mine both Ethereum and Sia as I have worked it out that Sia will pay for roughly 60% of the electricity bill. I believe my cards do have dual Bios as they are the Nitro version however before I do that I would like to know if anyone has settings for this card that work. I'd prefer not to experiment and guess. Thanks again.
It is great to hear. I have some AMD R9 390. When I do the dual mining, it uses a lot more electricity than solo.