Hi ScooterBob, if you mean engine vibes then its around 3,750rpm ie about 64mph real almost 70mph indicated.
But i"m sure that's not what you mean. In the old days an oscillation that quickly stopped was known as shaking its head where the end of the bars moved through about 2 inches.
A wobble lasted longer and was quite high frequency and was often cured by screwing down the steering damper. A BSA shooter I used to ride was prone to this.
The weave I describe is a low frequency oscillation. I haven't tried tugging on one bar or another as I feel unsettled enough, reduce grip on the bars allows it to diminish.
I'm starting to give it more throttle now and 60 in fourth gear isn't quite fast enough to induce the weave in an attempt to see if it could be rpm based, which I doubt.
If it is a rocking couple induced vibration then the resulting weave must be a harmonic produced by the frame. Being as the C5 is a new frame the symptoms it displays are similar to the early Triumph twins nick named Mr Whippy and let go for a whip round on the Triumph.
I can't remember which bike it was where lower frame members could be added to improve stiffness of frame by the swinging arm mountings, but wonder if this might be a quick fruitful line of experimentation.
It might have been XS 650 engines in BSA frames where the bottom frame rails were moved as it was thought the engine would provide enough stiffness, but don't quote me on this the memory is a bit hazy.
Sorry about the long reply, Shappers.