Thanks or all the replies, I didn't think it would be so complicated! The main reason for wanting to buy the Leupold is the weight saving and also i hear the optic quality is far superior to the Nikko but it sounds like a lot of money and hassle to achieve this. I didn't actually realise that there was no zoom on the Leups so thats another factor to consider.
I'm 37 and my eyes are pretty good so I don't think I need to worry about that, but I will defo try some Leups out at my club if the members will let me. I hear such good things about leupold but I guess I should maybe stick to my nikko til I try a few other non-leoplold and leupold scopes out.
Thanks again for all the responses.