The relation between excitation energy and reaction observables has been examined for (6.0-14.6)-GeV/c protons, (5.0-9.2)-GeV π-, and 8.0-GeV/c antiprotons incident on a 197Au target. Relative to proton and π- beams, 8.0-GeV/c antiprotons are found to be the most effective projectile for depositing high excitation energies in the targetlike residue. For protons and π- the excitation-energy distributions are nearly identical and appear to be independent of beam momentum above 6-8 GeV/c. It is found that total measured charge, total thermal energy, and total charged-particle multiplicity scale most directly with excitation energy, whereas IMF multiplicity and total transverse energy exhibit large fluctuations. Correlations of the observed fragment multiplicity, charge, and kinetic-energy distributions with excitation energy indicate a transition in the reaction observables near E*/A≈4-6 MeV. These experimental signals are consistent with a multifragmentation mechanism that becomes the dominant deexcitation mode above in the range E*/A ∼4-6 MeV.