The development team has seen insignificant changes in the delays over the temperature range for Virtex 5 FPGA. Hence, the speed files will show you the same result for each temperature. They did however see some differences when voltage was varied, so this is in the speed files.
Traditionally, with the older devices, differences were seen when temperature varied and not voltage. But now with the newer devices and smaller processes, the opposite is occurring. They are seeing differences when voltage is varied and not temperature.