pineteam,
Airbus recommends "aim to keep the speed in the region of the target speed, so as to provide the best protection against the effect of gust on the structural limits, whilst maintaining an adequate margin above VLS"(PRO-SUP-91-10 P 1/4).
The chart for Severe Turbulence on FCOM is identical to the one in the QRH.
CaptainProp is right. Severe Turbulence speed is 250kt from SL to FL200. Then is 280kt/M 0.76
Va ( Maneuvering Speed ) is a limitation. And it only applies when in alternate or direct law because in normal law you have protection. As per the graphic is from 256kt at SL ( is not linear ) to 300kt at FL295. Then 0.78M (FCOM LIM-13 P 2/6)