I've been doing a lot of testing I want to share some results I see a lot of people with similar issues where both cards are not being utilized. I am not using wattman as it limits you to 1.175mv so I am using MSI afterburner. I've noticed a problem with voltage related to GPU usage and performance. This 1st set of screen shots is with afterburner stock clocks for my cars 1303 core 2000 mem +50 power and +0mv=1.150
Now here is the results with nothing added except +50mv=1.200 as you can see it gained 10.5 fps and the gpu usage stayed at 100% much more often, of course with the added voltage comes higher temps.
So what it seems like is even at factory clocks for my MSI RX 480 Gaming X the card is not getting enough voltage at stock 1303 core 2000 mem so lets try stock rx 480 clocks of 1266 core 2000 mem with +50 power +0mv=1.150
So notice now the fps from the benchmark nearly matches the overclock of 1303 core yet this was 1266 at stock voltage and the gpu usage is really good. But maybe not perfect so we are going to try stock rx 480 1266 core 2000 mem +50 power but raise +25mv=1.175
Not much difference here from the +0mv=1.150 except we're using more power I'd say usage is about the same as the last test. Lets try 1266 core 2000 mem at +50 power +100mv
I couldn't complete this test due to the cards crashing. This is not a fix thread this is a discussion thread and results of my experiments. I am currently using revision 3 of the bios for the cards which there really is no details for but I've noticed the watts drawn is less so I'm going to put the 2nd revision back on the cards and will be back to post results. It definitely seems like the cards when in crossfire are just not drawing enough power to push the clocks barely at stock 1266 better yet at the 1303 they shipped with. Interestingly enough when 1 card is used separately this issue is non existent.