Quite an interesting thread to us NG operators and a lot of the comments and tips have been of value to us all I'm sure.
Just a personal observation, but I find that the "mechanics" of the flare technique remain similar whether it's a flaps30/40 landing. When winglets are thrown into the equation it mixes things up further still!!
But the ball park figure of flare once the 20 call has left your ears is what I apply whatever the flap setting or whether I'm flying with winglets or not.
What I vary, sometimes to a large degree, particularly in differing weather, is the point at which I start reducing power. Flaps 30 in a winglet aircraft with an element of tailwind means I'm reducing the power substantially earlier than I would when landing flap 40, non winglets with a 10 kt headwind!!