How did you jump to the conclusion that its your front control arms?
Run your finger up your disc brake rotor. if you feel a "lip" at the top then you have worn rotors which does usually cause vibrating from that speed...
Well our cars aren't BMWs... the mcpherson strut has nothing to do with the control arms... im almost certain its your rotor, do what i said above and let me know what you feel on the rotor.
I just had the rotors machined which fixed the issue. The front rotors were glazed over which is kind of weird since it doesn't get driven hard. Surprisingly, the brake pads were thicker than I thought.
If you are easy on your brakes,..glazing can occur. If you occassionaly apply heavy braking,..especially with "metal-king" type pads,..you'll cut into the cast-iron rotor effectively limiting glazing.
I had metal-king pads on a 351Cleveland LTD [the LTD in Oz is a normal sized car,..not a "Battle-Star Galactica" ] and the friction generated on the front rotors was so great [the car weighed 1.65T as it had LPG] there were small bright metal particles shed onto the wheels from the rotors...