At this stage you have determined that Xilinx® device is the most effective technology for your application. Now you need to define which family, device, package, speed, temp grade and voltage can best fit your functionality, performance, cost, and power budgets. In terms of power, you must estimate the total device power requirements even before any logic is developed. Understanding the total power requirements will help you define your power delivery and cooling system specifications.
For more information on power estimation, see Seven Steps to an Accurate Worst-Case Power Analysis using the Xilinx Power Estimator (XAPP1348).