Orpheus,
I haven't had this underclock issue, yet
Now, my 5870 is a Sapphire Vapor-X and comes overclocked a little from standard. When I saw a few weeks ago that someone was recommending AMD Overdrive - I turned it on and pushed the sliders up a bit. However, the last week at least, I turned it off.
Right now my CCC is for AMD Overdrive is set as follows:
Enable AMD OVerdrive = unchecked
High Performance GPU clock = 890MHz
High Performance Memory clock = 1260MHz
I have used the ATITrayTools monitoring graphs set to view Main CPU Usage and GPU Activity. My 5870 was running way over 80% - sometimes as high as 98% - during heavy load CoD application.
S!
Gunny