We report on striking sensitivity of the superconducting properties of ion-beam sputtered YBa2Cu3O6.9 films to the lattice disorder (induced by varying growth temperatures). Tc decreases with increasing disorder, while the width of the resistive transition and the normal state resistivity increase. We give a quantitative significance to this trend by expressing the degree of the disorder in terms of the lattice coherence length rc that is extracted from the width of X-ray diffraction rocking curves. We find that Tc saturates to the maximum of approximately equals 92 K for rcgt;10 nm.