Real-time beam-steering of highly directive antennas at mmWave spectrum under unpredictable propagation environments remains a highly elusive challenge for the upcoming 5G era. Reconfigurable and multifunctional mobile 5G antenna and RF architectures which are desired to achieve sufficient QoS introduce additional technical and economic costs which may outweigh the benefits. This paper investigates the effects and relative significance of key antenna design parameters with QoS benchmarks based on real-life mmWave antennas integrated in fully operable 5G mobile device prototypes.