Please do
Right I did not have time to do full tests as I was too busy setting up a new network but I did have chance to find out a couple of things.
I have a 5970 in slot 1 & a 5870 in slot 3. I have done this temporarily until I get my new water cooling to keep the cards cool. The problem with the current setup is that the 5870 runs at 8 rather than 16.
Anyway running with CrossFireX in single screen mode I am definatly getting good results ( not as good as it would be with 5870 @16 but good ).
I put desktop into eyefinity. 5760 x 1200 on 3 x 24 inch mons.
I run Dirt2 ( my usual testing software for eyefinity and CrossfireX ).
Usually at this stage Dirt2 runs at 20fps.. I must state I also get 20fps in BC2 with this setup also.
I ran the Diret2 Benchmark test and got 62fps av. All settings are maxed.
Now there are a couple of problems here and I need to test again with 5870 in slot 2 @ 16...reasons are as follows.
With just 5970 in Dirt2 I get 61fps av.
gpuZ is reporting 5870 is disabled ( shows this for extended desktop also ). However I know the 5870 is working in CrossFireX because if I run single screen I get at least 25% increase in score over single 5970 running heaven demo ( works out about right with 5870 only running @ 8 ).
So at the moment I cannot tell if the 5870 is actually being used in Dirt2 or not. I will do another test tonight ( if I get time ) with 5870 in slot 2 @ 16 but so far it is looking good that 10.4b has fixed the eyefinity problem.
I have also found posts elsewhere on net where others have stated this also
EDIT : btw forgot to mention in response to initial post. Another reason you cannot run quad 5970's is because the 5970 only has a single crossfire bridge plug whereas the 5870's etc have 2