The IAS 'steam gauge' in the panel can hardly differentiate between 350 and 400km/h but the V2 and Vref speeds are given with 3 digits. So either the PF give it a good margin or there is another clue on IAS I overlook. If the scan of the PF uses this IAS instrument as reference for TO then I can hardly imagine that they give margin to the low side operating the flaps. A TO mostly over water is routine and not very demanding as long as all donkeys work. The tower RT transcript sounds relaxed and not busy at all.
Has anyone the max. speed limits for the 15 and 28 degree flap settings at hand?