sluggish X.org/Xfce behavior

Hi,

since last weekend (November 17th) I have been noticing a sluggish
behavior of X.org/Xfce. Typical symptoms are:
- Alt-Tab not reacting all of the time
- pulldown/popup menus not allowing selections with mouse (typically in
Terminal/pidgin), or moving the mouse (touchpad) results in an automatic
click
- typing something in a Terminal requires mouse (touchpad) movements for
the text to show up
- sometimes moving the mouse (touchpad) is required for the laptop to
"wake up"; this is noticeable when Thunderbird downloads all messages
from the period when the laptop was "frozen".

I am running 10-amd64 r243234 (so with clang as cc) and ports 307851
without any local modifications. Since November 5 (when clang became cc)
I noticed x11/nvidia-driver and x11-drivers/xf86-input-mouse were
updated but rebuilding those with gcc did not make any difference. Maybe
I missed a related port? All ports last updated before November 5th are
still built with gcc.

My /etc/make.conf and /etc/rc.conf are attached.

Has anyone else been noticing this?

Regards,
René