A lot of people have been talking about this on the AMD forums. I've narrowed it down to this:
When the 4870X2 is run on a PCI-E 1.1 mobo (in my case P5K Deluxe) often times the driver reports a PCI 2.0 x1 slot, and [on board] crossfire is disabled. When booted in the x4 slot, it reads as a PCI 2.0 x4 (which is incorrect as well), but never does the x16 slot read as PCI-E 1.1 x16 or PCI-E 2.0 x16.
GPU-Z reports a PCI 2.0 x16 slot (which is wrong) and that crossfire is disabled when in the main slot (x16), and enabled when in the black slot (x4).
Running Vista 64 with 4GB DDR2-880
Any other findings?
I'm going to bench running in the x4 slot...
When the 4870X2 is run on a PCI-E 1.1 mobo (in my case P5K Deluxe) often times the driver reports a PCI 2.0 x1 slot, and [on board] crossfire is disabled. When booted in the x4 slot, it reads as a PCI 2.0 x4 (which is incorrect as well), but never does the x16 slot read as PCI-E 1.1 x16 or PCI-E 2.0 x16.
GPU-Z reports a PCI 2.0 x16 slot (which is wrong) and that crossfire is disabled when in the main slot (x16), and enabled when in the black slot (x4).
Running Vista 64 with 4GB DDR2-880
Any other findings?
I'm going to bench running in the x4 slot...