Ok, I will increase my clearance plane, manual only advises 3mm i think above fixed plate - thats what made me ask:)

The probe i am asking about is the one used when running the X & Y probing wizards - if the tool is grounded and the work (being metal) is grounded it cannot work, one needs to be isolated? Also the sides of an end-mill would not be accurate enough to probe an edge with?

I think 150mm is fine as thats all the Z i have.