Hi
Just been checking, and when in normal battlelog for BF4, my cpu usage is around 15-20 used, and quite a bit of memory. Switch to BF3, and the usage drops to around 0-5.
This is due, I think, to the moving image on BF4.
So, what I'm going to do for a while, is join a server as normal in BF4, then whilst its loading, switch to BF3, and then see if it drops the cpu usage.