I've been doing some other tests and I think I've isolated my two main issues and I hope (finger crossed) the most serious one is one (black screens). Yesterday I was using extensively my PC all day long, working in the morning, benchmarking in the afternoon and gaming in the evening and I *only* had flickering but no black screens.
Black screens issue:
At some point, I was able to reproduce those while benchmarking, but I think I was somehow causing that as I changed clock speeds and Voltage as I read was the solution for *some people* with similar problems on R9 290X (not 280X). So I reverted my clock speeds to stock (1100/1500/1.256V) and installed 14.10 drivers to start from there. I noticed that one of the "black screens" was happening because Windows 7 was changing colour scheme, so I disabled that. I said I was using some cheapo HDMI cables... so I replaced those with a brand new and better one. System was running fine (still with flickering) but I again decreased the stock clock speed a bit: 1000/1350. BIOS was latest: F4 (that is suitable for Rev 1.0 only)
Flickering issue:
It's still there. On these speeds: 1000/1350 flickering was still noticeable. Drivers were 14.10 (Catalyst 14.4). I tried a movie and screen was flickering nearly every 5 minutes or so. I ran Heaven Benchmark several times and left it alone for one hour, no artifacts or flicker recorded ( I use the webcam). I played one game for more than an hour, just one flicker happened on the menu, but never while playing. So I guess I am right now where most of the people stand with this issue.
Possible solutions to flickering:
There are several theories, based on what other vendors have done to fix the issue. In other forum, Gigabyte users claim that using 13.10 drivers (the ones that came in the CD) stops flickering for good. But this might not be a long term solution as we'll have to update drivers eventually. So here comes other ways to allegedly fix the issue while keeping newer drivers:
a) What Sapphire did with their BIOS was to alter Volt and max MHz for GPU and VRAM. This is essentially what user DW75 has posted, but instead of using a 7970 BIOS, using an actual R9 280X BIOS. This is just reducing OC to gain stability.
b) Other option is what deltaxi1867 says, and I think that has been used on others models (even on 7000 series) to fix this. It makes sense as most of the flickering occurs when card is on idle. So this fix consists of increasing min speed clock and in my case is 300MHz, so maybe 500MHz or other value in between should fix the problem.
Yesterday evening I did a fresh install of 13.10 drivers and left stock speeds (1100/1500 at 1.256V). It was late, but in the 40 mins I used the PC I didn't see any flickering. I played the same movie a bit and all fine so far...
Regarding BIOS changes: I was tempted to change it to a 7970, but I think that's risky if you don't use the exact compatible BIOS. Even for the same R9 280X card there are different versions with different VRAM (Elpida or Hynix) and different VRM controllers. Instead, we could modify our existing BIOS with a software called VBE 0.7 and set up a different stock clock.
