OP here....
Almost finally made up my mind.
Seriously considering going for the P45+ back.
Did a trip to Sydney in the past few days and dropped into L&P this morning, spent a few hours in there looking at my options.
I do have to go to Sydney again on Monday and intend to have a look at the Pentax 645Z ... but I'm sure my mind is made up.
I want to buy into a system that is versatile.
Buying a back and the body will enable me to also use the back on a technical body such as Alpa Cambo etc ... and having the phase One body and the Tech camera will also allow me to up grade to a higher back in time ... the P45+ will also hold value I feel, and upgrades from there will less painful once bought into the system.
Both cameras can also take the very best of lenses too, so upgrade options are available for both bodies in backs and lenses.