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:

Anyone can help me with updating my bios of a "Sapphire R9 280X OC Dual-X 3GB GDDR5 11221-07-20G"?

Here is the link.

https://docs.google.com/file/d/0B0h262BAwjKuaVNvaWt1bWJpS1U/edit?pli=1

There was no timing or VRM issue in this one, but as it is a previously unseen version: https://www.dropbox.com/s/vp6e4u9oqlemofy/Sapphire_E210400-OX2_AGR.zip

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?

orignal Bios Version : 015.041.000.000.000000
https://drive.google.com/file/d/0B-Zrpt5MaTNPQ0RSZmRyV3AwRE0/edit?usp=sharing

tryed
Sapphire_E21004_V44_K2_NT_AGR Bios Version : 015.039.000.001.000000
Sapphire_E210400-OX2_AGR Bios Version : 015.042.000.001.000000

got the same results

The VRM is probably overheating, a very common issue on recent Sapphire cards.
There is no timing issue with the original bios.

source: https://litecointalk.org/index.php?topic=12369.1215

And probably another related topic:
https://litecointalk.org/index.php?topic=13554.0