honestly even if you did manage to OD on benzos or xans specifically you probably wouldn't actually ctb. you'd feel like hell for a bit physically but success in ctb'ing via benzo OD isn't too common.
then again, I've been on prescribed benzos for 8 years now. a benzo OD wouldn't kill me but you might have more success.
if anything I'd say use the xans to calm the SI.