Interesting. You talking about the memory clock right?
My experience is exactly opposite of yours. Single monitor idle is 150. If I move a window around it'll jump to 1250 briefly.
With more than one screen active the mem clock jumps to 1250 and stays there.
This was true with my 3870x2, 5870 and 290x.
Yes, i am talking about the GPU MEMclock, no matter the number of screens i attach, the idle 2D memclock allways stayed at 150MHz.
But since crimson it tends to stay pegged at maximum clock of 1250MHz.
Offcourse when you are working sometimes it peeks to 1250 from 150 , that is normal and also not a constant 1250 but more like a constant 150. I'm ok with that normal behaviour.
Now with the new 17.4.1 , i have it comming down to 150MHz again at 2D/idle. Watching full HD vid on any of the screens now only ups the gpu clock and not the memclock , which seems in order as it should be. The Memclock only goes to 1250MHz during gaming or whatever work needs it.
However, strangest thing, when i do a "hot" reboot. The Memclock goes up to get stuck at a happy 1250MHz.
A subsequent shutdown and cold boot keeps the memclock back at 150MHz.
Some very strange stuff going on and i think it is still a driver problem. Seeing as to now the clock does come down again, I figure this has to do with the new WATTMAN stuff they put in, because practically useless for a 290X except reading some values...
You may be on to something regarding wattman. I use MSI Afterburner and have wattman disabled, actually never enabled. Maybe it's affecting the clocks?