I'd say 1066 was probably the middle period of Norman dominance with the invasion of England coming after the Norman expansion into Italy. I'd say you have a divergence of styles in different parts of the world, but the conical helm with nose guard and kite shield gradually faded from use over the next 50-100 years or so, with the helmet losing the nose guard and rounding out (also becoming the full helm) and the shield starting to flatten out at the top and become more like the heater shields of the 'high medieval' period.
Agreed, Sicily's definitely a bit of an odd case where a lot of different styles got incorporated!
If it helps in England at least, there's paintings and Manuscripts from just after the Anarchy that show the 'traditional' Norman look (nasal helms, mail hauberks, kite shields etc.) still in use, so you'd be covered for the mid-12th century at least, I think by the time the Third Crusade rolls around things change, but you should be covered for before then, at least into the 1150s!
