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[Display omitted] • Room temperature moduli of most Nb-alloys agree well with mole fraction weighted rule-of-mixture calculations. • A single, linear temperature dependence of the elastic properties is suggested for all Nb-alloys considered in this study. • A single Smith-Palmer equation adequately describes the thermal conductivity most of the Nb-based alloys investigated. • Thermal conductivity of WC-3009 is significantly lower than the thermal conductivity than the other Nb-alloys investigated. • A performance index is introduced for lightweight, panel-shaped applications subject to thermal gradients or transients. There is renewed interest in refractory alloys that possess higher service temperatures than incumbent Ni-based superalloys (⪆1100 °C). Thermophysical property data for six Nb-alloys are gathered from the literature and reviewed, and new data are provided for two Hf-containing Nb-alloys; elastic modulus, thermal expansion, thermal conductivity, and heat capacity are presented for C103, and new thermal conductivity data are provided for a higher strength alloy, WC-3009. Comparisons with Ni-superalloys and other refractory-metal based alloys provide context. Physics-based models are provided that describe the temperature dependencies of the Young's modulus, coefficient of thermal expansion and density, and thermal conductivity; such that fair comparisons can be made across alloys for any given condition. The results suggest a need for improved understanding of the temperature dependence of the elastic modulus. A performance index is introduced for making informed materials selection decisions in the context of lightweight, panel-shaped applications subjected to sharp thermal transients or steep thermal gradients, and the significant strain rate sensitivity of Nb-alloys is highlighted. Ultimately, the relative value of current commercial alloy, C103, as well as the promise of specific Nb-W-Zr alloys are highlighted. [ABSTRACT FROM AUTHOR]