After trying everything suggested in this thread and others, I decided to replace my mouse. The troublesome mouse was a Logitech G7 wireless mouse. I think my problem was intermittent and related to...

My mouse lag has come back today. I've already got the Realtek HDA driver v6.0.1.7724 installed. Guess I'll try the rename of the FMAPP.EXE file and see if that fixes it. Damn annoying.

Folks, I had the same issue, but for me the fix was to move my mouse (Logitech G7) from a USB2 to a USB3 port. Someone else in this thread said this. I realised that my problem had only just started...