Oxyborate single crystals, ReCa4O(BO3)3 (Re=La, Pr, Nd, Y. Gd), have recently been demonstrated to offer superior dielectric, piezoelectric and electromechanical properties to quartz, langasite and other commonly used piezoelectric crystals. Of particular significance is the ability to function at temperatures >1000°C, offering the potential for SAW, BAW and related sensors operational in harsh environments. In this work, the elasto-acoustic properties of oxyborate crystals were investigated as a function of rare earth cation. Crystallographic relationships were determined to be related to bond length and dependence of cation ordering, which was also reflected in the mechanical loss. Parameters related to high temperature operation, including electrical resistivity, dielectric loss, together with temperature dependent electromechanical and elastic properties were determined and discussed in relation to various applications.