The CrossfireX driver will allow you to make a quad Crossfire setup from one 3870X2 one 3870 and one 3850, but we are not sure how it will that compare in speed to four 3870’s in CrossfireX.
I am sure that enthusiasts will like it as this now means that despite the fact that you have a 3870 or a 3850, you can add unequal cards including the 3870 X2 and gain a lot of performance.
We can now definitely confirm that CrossfireX means a flexible way to use more than one card. However we are sure that you won’t be able to add more than four chips to work together and it remains to be seen if you’ll be able to mix these high end cards with 36×0 series or slower, which we sincerely doubt.
AMD CrossFire X to allow you to pair 3850s and 3870s
According to Fudzilla CrossFire X will be allow users to combine Radeon HD 3850s, 3870s and even 3870 X2s for up to four GPUs in a single system. That means that you can pair your shiny new 3870 X2 with your previous HD 3850 and get SOME KIND of benefit out of it. How much is still unknown, but we’ll be testing it soon enough.