  We assess the overall performance of our quantum key distribution (QKD)
system implementing the measurement-device-independent (MDI) protocol using
components with varying capabilities such as different single photon detectors
and qubit preparation hardware. We experimentally show that superconducting
nanowire single photon detectors allow QKD over a channel featuring 60 dB loss,
and QKD with more than 600 bits of secret key per second (not considering
finite key effects) over a 16 dB loss channel. This corresponds to 300 km and
80 km of standard telecommunication fiber, respectively. We also demonstrate
that the integration of our QKD system into FPGA-based hardware (instead of
state-of-the-art arbitrary waveform generators) does not impact on its
performance. Our investigation allows us to acquire an improved understanding
of the trade-offs between complexity, cost and system performance, which is
required for future customization of MDI-QKD. Given that our system can be
operated outside the laboratory over deployed fiber, we conclude that MDI-QKD
is a promising approach to information-theoretic secure key distribution.
