the effect of early vigor of F1 hybrids under low soil water content is the same as for CruiserTM Vigor Effect (R)(http://www.syngenta-us.com/media/emedia_kits/thiamethoxamvigorus/media/pdf/presentation.pdf) - such plants have better auxins transport to roots, roots grow faster, and will provide the plant more water from deep layers of soil. Such feature is neutral or even negative at normal water suplly.
We have got 2-year field data supporting such observation and had presentation on this subject at GLOBAL FORUM ON THE VIGOR EFFECT, 2009 Brazil, but Syngenta has not published this report.