Can i crossfire these two GPUs?

I believe its either the same series with AMD, or the same first 2 number, so like any 78** can crossfire with any 78** its one of the 2. I could be wrong but I'm sure it will work.

Yes I believe you can Crossfire those two cards.
You can Crossfire any AMD card as long as the first two numbers of the cards are the same. In your case, 7870 and 7850 = 78 and 78 Yes, I believe you can.

Cheers  

Well, there are exceptions. The recently released 7870 JokerCard cannot be Crossfired with regular 7870 or 7850.

Your 7870 will perform at the spec of your 7850 when you crossfire them



Don't get me started on that idiocy  .

Yeah, AMD announed a line of 7870's that are based on the tahiti architecture, which makes the card physically a de-tuned 7950 instead of an actual 7800 series card. This is why it won't crossfire with a 7800 series card.

They wanted a card priced in between the 7870 and the 7950. It was stupid, and they didn't release a refererence card and only a few manufacturers actually made this card. Club 3d's version was called the Joker card (aptly named, imo).

The Tahiti 7870's may actually crossfire with a 7950, though.