To get a specific refresh rate, I'd add a Modeline to the Monitor section (and check HorizSync and VertRefresh are correct). To get a valid Modeline, you can either pinch it from the xorg.conf of a distro that autodetects your monitor settings properly or generate one using the online Modeline tool.
http://www.bohne-lang.de/spec/linux/modeline/eg.
Modes "1680x1050" "1280x1024" "1152x864" "1024x768" "800x600"
Modeline "1024x768" 81.54 1024 1064 1168 1352 768 768 770 804
EDIT: Wrote the post in the morning when half-braindead, re-read and realised I'd completely branched off the original question. Fixed.