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 compare in speed to four 3870s 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 36x0 series or slower, which we sincerely doubt.