Can two ultrarelativistic objects lose almost all their energy to gravitational radiation?

In 2007, Pretorius and Khurana [Black hole mergers unstable circular orbits, Classical Quantum Gravity 24, S83 (2007).] did ``speculate that at threshold [at a critical impact parameter], all of the kinetic energy system [two ultrarelativistic black holes] is converted to gravitational waves, which can be an arbitrarily large fraction total energy.'' However, in 2012, Sperhake et al. [Universality, Maximum Radiation Absorption High-Energy Collisions Black Holes with Spin, Phys. Rev. Lett. 111, 041101 (2013).] performed numerical calculations led them contrary conclusion: ``An extrapolation our results limit $\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\infty}$ suggests about half center-of-mass emitted radiation, while rest must into rest-mass spin Here I present arguments against this latter conclusion support earlier speculation for sufficiently $\ensuremath{\gamma}$, but small radiated away as waves.