High-speed wireless backbones have the potential to replace or complement wired connections. This paper provides a comprehensive network and transport layer performance evaluation of the Magnets WiFi backbone. The backbone, deployed in a metropolitan area of Berlin, consists of six 108 Mbps capable links using directional antennas and spans over 2.3 km. Built with off-theshelf hardware, it features mixed 802.11a/g technology, link distances between 330 m and 930 m and support for two enhanced MAC/PHY layer modes at the access points (AP) to improve their performance. These unique characteristics provide a challenging environment to investigate the impact of a wide range of parameters. In particular, using CBR and VBR traffic profiles, we assess the influence of distance, 802.11 technology and AP modes on throughput, delay, packet loss and jitter between pairs of adjacent nodes. For example, our measurements show that the average UDP throughput of the 802.11g links varies between 15...