The 9000 is a very old machine for which parts are increasingly in short supply...I would strongly advise the Ziehm on that basis alone. The Ziehm should work fine as long as you go "easy on the pedal" and do not use protracted continuous real time high amplitude (mA) exposures which will burn out the anode. For vertebroplasty, the Ziehm may be insufficient due to this limitation (no rotating anode to disperse the heat to avoid anode deformation and pitting).
FYI: The OEC 9400 will no longer have original manufacturer parts available after this year, ostensibly part of the planned obscelescence of expensive machines by OEC, although the machines have not been manufactered for 15 years now, so their withdrawal from parts manufacturing is probably justified.