WHILE ONLY THREE RADIO BRIGHT Z>5 MASSIVE (>10^9 MSUN) BLAZARS (AGN WITH JETS BEAMED AT EARTH) ARE KNOWN ESTIMATES OF THEIR BULK LORENTZ FACTORS (GAMMA) GAVE GAMMA>10. THUS BEAMING CORRECTIONS IMPLIED SEVERAL HUNDRED BLAZARS AT Z>5 WITH IMPORTANT IMPLICATIONS FOR THE EARLY GROWTH AND SPIN EVOLUTION OF MASSIVE BLACK HOLES. HOWEVER OUR NEW FERMI ANALYSIS GIVES SMALLER GAMMA AND HIGH-Z POPULATION. TIGHTENING THE MEASUREMENT FOR THE BEST AND BRIGHTEST OF THESE SOURCES J0906+6930 (Z=5.48) IS OUR GOAL. WE HAVE ASSEMBLED THE OTHER REQUISITE SED COMPONENTS; THE LAST MISSING PIECE IS A SENSITIVE HARD X-RAY SPECTRUM. A 100-KS NUSTAR EXPOSURE SUFFICES TO MEASURE OR TIGHTLY BOUND THE EXTERNAL COMPTON COMPONENT FLUX AND THE RELATIVISTIC DOPPLER FACTOR FOR THIS HIGHEST REDSHIFT BLAZAR SOURCE.