Mixing Brands

Hi everyone. I've lurked the forums and reviews for a while now but this is my first time posting here. I currently own this GPU and I'm getting the urge to upgrade. Now, I don't want to replace the card cause I'm out 300 something or more just to get a small improvement and then I have GPU just sitting around. What I would like to do is xfire but every sapphire 5850 I find is too expensive compared to other brands. So what I would like to do is purchase another brand of 5850 and xfire. My question is, can I do this? What matters when doin this? I'm assuming they need the same memory specs (DDR5 256-bit 4000 MHz) but what about everything else? Here is an example of another card I looked up.

Thanks in advance!

It should be fine to Crossfire different brand cards together as long as they're the same model and have the same amount of memory.

That's what I was thinking. Okay, I'll make sure to keep that in mind. Thanks for the help.