I/O mezzanines promise flexibility and a reduced system footprint. Most mezzanines use standard bus based interfaces or a proprietary format. Aimed at FPGA centric solutions, the FMC (FPGA Mezzanine Card- ANSI VITA 57.1), is different. In the same way as one might strip out unnecessary weight in a car aimed for racing, the FMC is a performance solution that strips away unnecessary generic interfaces for direct FPGA driven I/O. But that requires knowledge to achieve the desired performance and to ensure the host and FMC module will work well together. This paper outlines some of the considerations in order to assess and the ensure that the host and module will integrate.