Thank you again for suggestions.
@sparrow: "... then you're probably not going to get any screen to work accurately, reflections and the constantly changing ambient light throughout the day will make it impossible I fear"
It's a correct observation, I know this, when working on photos I close the window behind the desk in order to avoid any changing in the ambient light. It' s a must! It will be an almost dark room!
By the way I notice when I print (hpb 9180) after a time without printing each time I have to "learn" a little the relation between the screen image and the print. Not easy to find the correct words in english, I mean I make 2/3 test prints, when I find the one which works I can visually see how to correct the other files in order to have a consistent result. Than I can easily print a batch.
@ phantomas: yes, I know ram from apple is very expensive, there are alternatives, only the warranty...in Italy delivery from apple store for a configured i.mac as we are discussing here it is about 4 weeks, maybe more...
My actual i.mac is 6 years old and I'll keep it anyway to run snow-leopard and the nikon scan software, and for emergency ...