I checked the xorg log file and found, that the Cirrus card emulation apparently has no DDC channel implemented, thus cannot detect the monitor and then X.org falls back to a plain SVGA monitor. From the logfile:
Using default hsync range of 31.50-37.90 kHz
Using default vrefresh range of 50.00-70.00 Hz
Simply setting those ranges to something reasonable (I got my values from "
hwinfo --monitor") helps quite a lot. Put this into /etc/X11/xorg.conf.d/50-monitor.conf:
HorizSync 31 - 61and you get a much more usable 1024x768 resolution.
VertRefresh 50 - 90