Hey Ren and welcome to CS!
Your selections are all good machines and I can assist with the Giotto and Minore. You may also like to have a look at the Diadema Junior plus semi-auto....Its a superb machine.
Its not that unusual to have special models for OZ and it wouldnt surprise ma if thats the case with Vibiemme.
As for gauges, the 2nd gauge on the minore gives "an indication" of pump pressure....I have found that they are within a bar or so of actual group head pressure. The important thing is to have a machine which is bench tested by a professional and adjustments where required made to ensure that the machine operates at optimum pressures.
I have demos of the Diadema and Expobar and expect a new Giotto demo this week (had to selll the previous one :() if youd like to comae and have a look/play...