These girls def have a "vibe spot." Mine is around 4300 RPMS (about 82-83 MPH in 6th). You can feel it coming, intensify, and then subside as you rev through this RPM spot (by 90 MPH in 6th, it's pretty much gone). It's easy to avoid vibe side effects by simply not riding in the vibe spot. I can cruise all day long at 80 MPH (6th gear) with no worries. There have been times however where traffic forces me to either ride between gears, or around the vibe spot RPMS (in which case I have noticed some vibe sensations in the foot pegs).
D