I bought 2 new Sapphire R9 280X TOXIC and I have problem with hashrate.

In those cards is new bios version 015.043.000.005.000000
Im able to get max 600 khash on it.

I have also 18x other TOXICS with BIOS 015.041.000.000.000000, and I get 760-800 khas without any problem.

I've tried to flash bios to the old one but cards doesnt accept it.

Any ideas ?