Seems to be some confusion between clean and flap-down Vx. If taking off with flap, use the appropriate Vx (or Vy), which is will certainly be less than the clean Vx (or Vy).
As Capt Nomad said, the manufacturer provides the best numbers to use. In light Cessna and Piper aircraft, the manufacturer's quoted TOSS's are actually pretty close to Vx anyway for that configuration. (Not quite identical though.)
In light aircraft I generally found that the attitude for Vx (or Vy) climbs was very similar across all take-off flap settings, once clear of ground effect. Very helpful if you want to avoid chasing the airspeed indicator in a steady climb.
Now in those immortal words from Capt to FO: "take off flap please".