I have a Radeon 5850 one of the first http://www.hisdigital.com/us/product2-474.shtml
its deactivated or not available on major computer hardware e-shops
so I was wondering if I am able to crossfire that with another 5850 of a different brand say, or Sapphire?
or is it possible to even go 5850 crossfired with 5870?
I believe yes you could crossfire two different brands as long as they can both have crossfire capability and are the same model. Now using crossfire with different models depends on the numbering scheme I believe. To answer your question, yes you could crossfire the 5850 with a 5870; however, both cards will run at the 5850 clock speed if I understand it correctly. I hope that helps