As this issue seems to have been resolved with new drivers I'll mark this thread as solved now.
For the first time since China Rising was released, I have just played 10 straight games without a single memory leak incident.
For me (at least) it looks like the "Windows 8.1 Update 1" (released on 8th April) has fixed it, or at least "reset" whatever was causing it to happen.
http://www.microsoft.com/en-us/download/details.aspx?id=42335
Update: Spoke too soon. Memory leak still, although it took a LOT more games than before to occur so it has improved to some degree. Also this time Windows actually crashed the game with a DirectX error and teminated the program. I haven't had it do that before, usually it just runs slow until it becomes unuseable, now it kills the game. Still need to reboot to clear the memory though.
