Athough much less likely, are you confident of your wheel balance? Typically you see the problem come up at 62, 72, 82, etc.,
but once in a while, a weight comes off, and the problem seems to be worse at one particular speed. It would be cheaper
to check this first, but as I said, it's much less likely IMHO than a problem with the struts or geometry.
Just covering all the bases. ;)