Continous pings with different packet sizes (at least 10000 pings) are valid tests for performance (response time and packet loss) of a new circuit. You should not have more than 1% packet loss (obviously I don't what response time would be acceptable). The only thing you can not perform from the router, is a stresstest (fully load the circuit and observe the performance under full load). This requires specialized equipment and software.
HTH, Thomas
