From what I understand make sure the RZ is as late a model as possible. The early ones had a serial number that started with the letter "H". I was told (repair guy) that RZ's had refinements along the way. The electronics will be newer too, which is good. I have an "H" which is fine, but the mirror coming up when I fire it seems quite a bit harsher than the later ones I have tried. Other than that it's an amazing camera whether it's an RZ or Pro II
Save the money from buying the RZ67 Pro and put it towards another lens or the very useful combination of Left Grip (with shutter release) and Winder.
I have both types of RZ and in practical terms there's nothing to choose between them - I've never needed the fine focusing capability when using the old cameras and only once on the ProII with a tricky macro shot using the tilt/shift adapter. The older RZ represents one of the true bargains in second-hand gear.