Anybode else got that problem?
Starting ATI Stream application on both cores of 4870x2 results in that only first core goes from 2D to 3D mode and so running at 750Mhz clock rate while 2nd core stays in 2D mode with only 507Mhz speed.
2nd core can be forced to run with 750Mhz clock rate simply by starting in parallel some 3D application so driver starts to think that it needs both cores at max speed, not only first.
I guess it's another driver issue...
What is your os and driver version?
I have got the opposite situation to yours. I have dual 4870x2 cards in my system. When I run an application on one card, the frequencies of the other three cards always reach 750MHz simultaneously.
My os is opensuse 10.3 with 64bit Linux driver 9.6.
Windows Vista 64 & Catalyst 9.6.
I have some feeling that earlier situation with Windows was exactly the same as you described and now it got "fixed" in such weird way...
Might this have something to do with Crossfire being enabled?
In Windows XP, you have to enable crossfire to make CAL recognize two cards. Maybe it is true for Vista. I am not sure, just have a try.
There no problem with cards recognition, problem is that driver doesn't counts 2D applications as ones who can utilize both cores at 100%, that's why 2nd core stays in 2D/507Mhz mode.