Crossfire / CrossfireX help needed

[g0reDon]

 hi everybody,

atm i'm using my gaming PC, i5-3570K at MSI Z77 MPower Mainboard and ASUS EAH5870 Voltage Tweak GPU.
no i want to build a little rig, max 3 GPUs are possible.

unfortunatelly it is hard for me to find the same card that fast... but i could buy tomorrow 2 different 7950-models, each at 219€:
Gigabyte Radeon HD 7950 WindForce 3x  and VTX3D Radeon HD 7950 X-Edition  

can 2 or 3 same chip but different vendor cards work at near to maximum each?

thx for any awnsers

edit: spell correction

[Gabi]

Crossfire is useless for mining.

[g0reDon]

but it's possible to mine with more then one GPU at one mainboard...

so i guess the technic is called otherway, but at least the question still stands: can i use both cards at same time, for example mining each at different pools? or have them to be same cards, same bios ect.... ?

or is it maybe even possible to run my 5870 and 1 or 2 7950s at sametime effective?