Quality of the CCF vs. wavelength range. Left (top, solid lines): comparison of a green and a red CCF of UZ Sct based on the same FEROS spectrum as well as the comparison of a blue and a red CCF of BG Cru (bottom; dashed lines) based on UVES spectra acquired at the same observation epoch with the blue and red arms of UVES, respectively. The bottom UVES CCFs have been shifted downwards for clarity. Middle: histogram of the CCF quality factor Q averaged over the pulsation period P for each studied Cepheid (green: six FEROS and HERMES targets; blue: 24 UVES blue arm targets; red: 30 FEROS, HERMES, and UVES red arm targets; see text). Right: same, but for the histogram of our S/N_CCF proxy averaged over P for each target.