DE-FACTO,
The speeds that may be generated by some FMS systems or from the QRH are not optimized and are not taking into account things like runway slope, obstacles etc.
To get the RTOW charts out (if you have them, if you have LPC laptop you won't) would take just as long as starting up the laptop and cross checking the numbers.
Airbus specifically warns that the speeds must not be mixed and matched, so best to take a moment and update the FMGS with the updated information.