I don't remember off the top of my head but we generally use 10% of the height as a limit. As long as the wire does not blow out past the edge of the right of way when you consider the deflection of the pole along with the wire displacement under a high wind case or the NESC 6 PSF wind speed, then I don't really care structurally what the deflection of the pole is. Assuming you use steel poles and not fiberglass and the slip joint uses the ASCE 48 minimum distance, then there should not be a problem with the slip joint failing.

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I have been called "A storehouse of worthless information" many times.