Isn't this one of those famous NV surround quirks where all displays don't have the same sync rate and such? He is using nvidia's and different monitors. Don't know enough about that myself as I use ATI, but it might be something you want to look after in your quest in solving this problem.
What you could also experience is the acceleration kicking in. It is weird however you only notice this in the full resolution, as that would be a problem across the board I think.
I always apply MarkC's mousefix;
link when I install my system to avoid this. Especially Call of Duty has this bad with high DPI mouses. However I don't think this is it as it doesn't occur when you are in a lower resolution.
What I recently had with my logitech g500; Next to mouse lag I had "lag" across the entire system due to usbport.sys having incredibly high DPC execution times. When you get that mouse lag, does sound "skip" or "drag" for a second? Or does it seem like you have a lot of packet loss (while you know that can't be the case)