Not tried it myself, but see my post above. Someone tried some different roms, but there were no changes for this new sapphire revision. Some actually give worse results.
I am now getting about 730 kh/s on mine, using TC 8193, gpu clock 1065, memory clock 1500. Staying at 72-73C at the moment. Also lowered my screen res to 1024x768, and made sure what is displaying on the screen is static. As soon as something is moving (cgminer window, or whatever) the hashes go down to about 690. Yes, I know, crazy.
With those exact settings I get 717 Kh/s, so it's a bit better than before. First setting where a clock above 1050 isn't counterproductive.
Same card, same bios, same problem. Can't get above 708 Kh/s with this card and a engine clock of anything above 1050 lowers the hashrate. Card gets 64C, but can't read the VRM temps as there are no VRM sensors anymore. Thinking of returning this card if there isn't a fix available.
Some more people seem to think the problem is the VRMs. This is probably a related post on a different forum:
Hi, I got the same card i've used your bios linked, no changes, if i go over engine 1050 / memory 1500 hasrate down
i've try the vapor-x version too
Quote
Sapphire Radeon R9 280X Dual-X 3G GDDR5 OC UEFI Edition (11221-07-20G) Elpida EDW2032BBBG Try this one, it should work. It is the Vapor-X bios which has 20MHz higher engine clock. There should be no throttling as the VRM temperatures are around 20°C lower. https://www.dropbox.com/s/j584q8qh0rd6hyv/Sapphire_E21004_V44_K2_NT_AGR_ELP.zip
got the same perf and same pb going over 1050 / 1500 is there a way to boost those card?