Hello people!

I have been given the go ahead to start some tentative moves towards a vanilla network from CC4

I have done a little research, and see that there are three ways I can do this:

1) One big jump from CC4 to Vanilla - This is almost a complete no go for the amount of disruption and the need for bringing in extra help at substantial cost
2) Creating a new domain, setting up a trust relationship and then moving groups of computers across room by room.
3) Keeping the existing domain, but starting new OUs (with inheritance blocked) and moving the various machines and users across this way.

At a glance, number 3 looks like a low risk\easier method, but is there any advantage in going for a brand new domain? Also for those who have done this before, is there any major gotchas I need to be aware of?

Thanks in advance