In the last few years, there has been an increasing awareness of the need to evaluate new mobile applications and protocols in realistic wireless settings, and platforms such as the GENI WiMAX testbeds have been developed to fulfill this need. However, wireless testbed users have experienced frustration when straightforward usage scenarios do not consistently agree with the high data rates that are advertised by the wireless technology. This work seeks to clarify the performance characteristics of two GENI WiMAX testbeds under various wireless signal conditions and network traffic patterns. By measuring the performance of several popular wireless Internet applications in two very different wireless environments, we gain a deeper understanding of how a researcher may expect the GENI WiMAX platform to behave. Our findings include some counterintuitive results, e.g. that increasing signal quality can reduce application throughput, and that applications using a single TCP flow may achieve as much as 72% less throughput than an application in an identical setting that uses multiple TCP flows. With this work, we hope to help other researchers design realistic experiments on wireless Internet systems, understand the perceived shortcomings of the GENI WiMAX platform, and interpret their experimental results in the context of the wireless setting in which the experiment was conducted.