In this paper, we present experimental evaluations of operating speed, power consumption and chip temperature with load fluctuation on commercial FPGAs. The measurement results show that operating speed is decreasing 16% with 142 ring oscillators as load circuits. Furthermore, operating speed depends on the mapped location in an FPGA chip, and the speed variation range is 1.8% to 7.1%. We also evaluate die-to-die operation speed variations using another FPGA board. The measurement results indicated that there exists indispensable speed variation of 11.9%.