I don't think even Hybrid Crossfire will allow that much of a difference, though I'm not totally sure. I think it was meant to be same card, different clock speeds or something.
If running in DX10 mode yes, but in DX9 mode that conflict wouldn't exist. I really don't think it will work, perhaps a HD3850 and HD3870 would though. Still, it's worth a shot.
You are about to answer a thread that has been inactive for more than 6 months. If you still wish to proceed, please ensure that your posting is original and does not duplicate or overlap any prior responses to this thread.