FoM for the 3 surveys as a function of the SN statistics in DESIRE. The upper horizontal scale is the fraction of events actually entering into the Hubble diagram, with respect to our baseline assumptions. Event rate measurements at z> 1 (see Sect. 3.3) suggest higher statistics (by ~20%) than we assumed, and the efficiency at getting host redshifts could eliminate 25% of the events. In any case, we see that the cosmological performance does not depend critically on these numbers.