I have tested three compatible 580 nitro bios with my 590 nitro, two of them where working without problems and driver patch isn't needed when doing a bios mod, with the 590 is needed.
The problem I see is that I can't reach my stock 1545mhz core clock with the same voltage. So maybe they have done some improvements to the 590 bioses to gain highest core clocks, or maybe into drivers.
I remember that some one have tested a 590 bios into a 580 without success, in this thread or the polaris bios mod thread.
I think that maybe the cause could be that 590 bioses have much lower voltages for the same clocks than the 580 ones.
Also it seems that the worst 580 comes with lower clocks like 1340mhz vs 1411 or 1450 for the good ones.
But on the 590 gpus the differences bettwen clocks are lower, 1545mhz to 1580, and they are using powerplay usCKSOffsetandDisable values to adjust the voltages. The values are bettwen D and 32 (on 580 bioes are 0), so the default voltages are increased between +12.5mv and +50mv.
So if you know anybody how wants to test or anybody here wants to test a 590 bios into a 580, 570 or 480, 470, I think it's bettes to use the bioses with the highest usCKSOffsetandDisable values, and decrease the clocks to the 580 stock ones , or maybe lower, and then adjust the clocks and usCKSOffsetandDisable values.
about using a 590 bios for 480 or 470 gpus, it could be more difficult as 590 have diferent values for vddci into voltage object info table and asic init table. So some changes into this tables will be have to be maded. My 590 have the same config as the 580 one, so using a 590 bios into a 580 could be easy.
Also I think some of this thread 480 to 580 bioses conversion have some mistakes in the vddci configuration. Hellm knows it, but the problem is that you have to use a multimeter to know vddci values, so it will be helpfull if somebody have one and can test it.
I have tried the bios name conversion from 590 to 580, only the stock 590 bios named to 580. And it can be done changing E6 01 to E6 07 and Polaris30 to 20. But I have black screens in games with the stock clocks, I have to test if with lower clocks if it's ok.
I also have tried the stock 590 bios named to 480 changing E6 01 to C6 07 and and Polaris30 to ELLESMERE, but it is reconiced like a 580.
So maybe the drivers is doing some thing to the 590 gpus to can achieve higher clocks or some feature is needed for the 590.
I have tested the stock 590 bios named to 580 with 1500mhz instead of the stock 1545mhz and is working ok. I don't have tested how near to 1545mhz I can go and I think that is not wort to test it. The gpu should be stable with the stock cloks. So for bios moding it seems that is better to use the driver patch than the rename to 580 or using a 580 bios, at least untill it don't stops working.