I currently am using the 1 gig Radeon HD 5870 and was wondering if it is possible to crossfire it with the 2 gig eyefinity version. I know SLI lets you combine cards with different memory values with their coolbit technology. Is it the same for ATI? Also, is eyefinity take advantage of multiple GPUs?
Yes, you should be able to crossfire with the 2gb version. It will default to using only the smallest frame buffer, or 1 GB for each card. So paying extra for extra memory really won't do you any good.
Crossfire would be beneficial at higher resolutions. I guess it would depend on how many monitors you are driving and at what resolution. but if you have the money to spend, why not?
With crossfire(I believe SLI as well) you can use cards with different amounts of memory but the card with more memory will not use more than the other. So if you get the 2 gb card will only use more than 1gb when used on its own, not in crossfire with your current card.