Published in Graphics
Faulty Sapphire HD 5770 BIOS disables 80 shaders
There's still 720 to go around though
A BIOS glitch in Sapphire HD 5770 Vapor-X cards seems to be responsible disabling 80 shaders, dropping their number to a total 720, which is what you get on an HD 5750.
Although the shader count is slightly lower, the clocks were not affected, or any other part of the card for that matter. According to Techpowerup, affected cards use BIOS version 012.014.000.004 and it is possible to use a different BIOS version (012.013.000.001.034705) and unlock the full 800 shaders.
You can do it yourself, or you can get in touch with Sapphire support and it's probably a good idea to do so, as you shouldn't fiddle with the card's BIOS unless you know what you are doing.