performance drop after crossfire bridge (and removal)

[martin.po21]

Helo

Heart of my rig are 4x HD5970.
I am using oclHashcat 1.32

I have problem with performance drop, which occured right after trying with crossfire bridge.

Before crossfire WPA speed 636xxx h/s
After crossfire + crossfire removed WPA speed 505xxx h/s

Can anyone explain to me what happened please? Google failed me.
At first i taught that gfx bios may become modified due to crossfire bridge installation, but card clocks stayed the same (core MHz: 725, memory MHz: 1000)

GPU load was in both cases 99%

Any idea how can I reverse this?
It is enormeous performance drop, which i simply can not ignore.

Thank you!

[martin.po21]

Problem solved with hdd format.