Spectral hole burning material parameters that impact optical memory architecture and performance are investigated. Optical power budget analysis for the data storage process reveals that although narrow homogeneous linewidth can confer high data density, it does not optimally support high data rates. Trading narrow linewidth for higher oscillator strength would be desirable, if attainable. Experimental measurement of oscillator strengths, quantum yield into alternative hyperfine ground state levels, and persistence of the hyperfine level populations in Eu3+:Y2SiO5 and Pr3+:Y2SiO5 are presented and discussed. Quantum yield measurements of less than 25% indicate that spin projections are strongly preserved during excitation and relaxation processes. The hole depth consequently attainable from single π-pulse illumination requires trade-offs in memory system design.