We describe the use of a reconfigurable board to obtain information on the performance that can be expected on particular systems. Our goal is to use the reconfigurability, of the board's interface to test a system and discover not only the maximum bandwidth and best latency attainable, but also the way to reliably achieve these figures. The board we present uses the now widespread PCI bus. PCI is sufficiently complex, and its implementations sufficiently varied, that it is impossible to guess the performance that can be obtained by a specific board on a specific computer with the only technical characteristics of the two in hand. We observe astonishing performance differences between almost identical systems and comparable figures between small PCs and big servers. Our performance tests can be an end in themselves, however, they also serve to demonstrate the value of a reconfigurable bus interface. With the same board, we can test and choose a system, make informed architectural decisions on the hardware/software interface, and then finely tune the bus interface to get maximum and predictable figures in the running application.