In the 100 fly I take 7-8 kicks off the walls. I breathe most strokes, though not because of the SDKs (I have just found that it doesn't slow me down). Here is a clip from the floswimming from Clovis nationals last year (I'm in lane 5):
In the 200 fly, currently I take 6 kicks off the walls on the first 100, then 5 kicks on the second. Clovis clip (again, lane 5):
I do more kicks on backstroke, but it isn't because oxygen debt is less of a problem: actually it is worse in backstroke than fly b/c of the flipturn. I am simply faster at SDK on my back, and I believe my butterfly swim is a little faster than my backstroke swim. Combine the two, and it makes more sense to take 1-2 fewer kicks off the walls in my fly races.
In practices I never take fewer than 5 kicks off the wall on fly sets, no matter the distance. As Ahelee says, there is a big psychological component (though I also think there is some physiological adaptation): at this point, doing fewer than 5 kicks feels very odd to me.