The VIVACE converter enhances VIV to harness horizontal hydrokinetic energy of water flows. High-Reynolds and high-damping are required to operate VIVACE in ocean/river currents. Scarce VIV data exist in that parametric subspace. Tests are performed for Reynolds number 40,000<Re<120,000 and damping 0<ζ<0.16 in the Low Turbulence Free Surface Water Channel of the Marine Renewable Energy Laboratory at the University of Michigan. Extensive testing was made possible by building a virtual damper-spring apparatus, which has been system identified and verified with real damper-spring tests. Thus, damping and stiffness are adjusted by software rather than hardware. From the VIV tests, the optimal damping for energy harnessing was found for velocity 0.40 m/s<U<1.10 m/s using spring stiffness 400 N/m<k<1800 N/m. Thus, the VIVACE converter power envelope is developed. The following experimental observations are made: (1) In the high-lift TrSL3 and TrBL0 flow regimes, high-amplitude, high-damping VIV is maintained. (2) VIV strongly depends on Reynolds. (3) The amplitude ratio (A/D) increases with Reynolds number within the upper branch of the VIV synchronization range. (4) In TrSL3/TrBL0, A/D of 1.78 was achieved for a smooth cylinder routinely in low damping. (5) Power density of 98.2 W/m3 at 1.03 m/s (2 knots) is achieved including space between cylinders.