Root Rooted MT3G Preparation for 2.2

[Monsignor]

Hi all-

I have a MyTouch 3G (original not Fender to the one with the 3mm headphone jack) and is rooted and running a Cyanogen 5.x ROM. My Nexus One arrived today and I am going to give the MT3G to my wife... question is - I want to unroot for her in anticipation of the 2.2 coming (allegedly). Should I be at 1.5 or 1.6 for this?

Any ideas?

Thanks in advance.