Hah, wow.
So it happens when it's playing a game in a different resolution to the desktop?
I'll have to go from 1360x768 to.... 1366x768. I didn't even notice they were different. Hopefully that'll fix it.
I also found this thread on Relic's CoH forums, so it may not be totally the fault of Windows here;
http://community.companyofheroes.com/forum/company-of-heroes-2/company-of-heroes-2-general-discussion/company-of-heroes-2-bug-reporting/61672-investigating-a-memory-issue
It might be a CoH2 problem but its likely this Windows 8.1 bug. Hopefully that change fixes it for you. It's an awful memory leak triggered by running programs full-screen in non-native resolution, and hasn't been fixed since the release of 8.1, though supposedly Microsoft has now acknowledged its existence and is working on it.
The same thing has been happening to me and my systems specs are quite similar to yours. Hope they fix this soon it's making coh2 nigh unplayable
Are you on Windows 8.1 too?