I just had a curious question to ask. I have an Asus Rampage II Gene and I am running two 5850's in CrossFireX on the two x16 slots. I also have an Nvidia GTS250 running on the x4 slot for dedicated PhysX which works rather well. I am able to fit all three cards on my motherboard because I use a 12 inch PCI-Express ribbon cable that allows me to move the GTS 250 away from the motherboard.
So my question is, would it be possible to connect a third 5850 on the x4 slot and do x16/x16/x4 5850 TriFireX?
From what I have seen the x4 slot is sufficient enough to run a graphics card with minimal performance compared to x16 and x8, but also wouldn't effect the performance of TriFireX either according to reviews.
The reason I would like to do this is that PhysX is nice and all but so few games I play utilize PhysX and I would get more use from a TriFireX configuration. Plus with the ATI 6000 series right around the corner there should be some price drops in the 5000 series cards coming.
Just as a side note, I am upgrading this Asus Rampage II Gene to the Asus Rampage III Gene shortly so the GTS250 would go with the Asus Rampage II Gene and a 9800 GT for dedicated PhysX in a second system.
Yes you can use another 5850 in the x4 slot, but Tri-CrossfireX doesn't scale as good as 2 cards,i mean in some games you may get a good performance boost but in some you may not,its because of the drivers(and also some games don't benefit from CrossFire).