Comparison of C IV FWHM and C IV-Mg II velocity shift for our sample, for the z > 5.8 quasars from Schindler et al. (2020), and for the SDSS DR7 quasars from Shen et al. (2011), for which the C IV-Mg II velocity shifts are calculated in Shen et al. (2016). The quantities on the x- and y-axis refer to emission line properties, while our dataset is colour-coded according to the presence or absence of absorption features, either C IV+N V NALs (teal stars) or a C IV BALs (teal diamonds). Quasars with a BAL trough do not typically present C IV+N V NALs. There is only one exception in our sample displaying both, J1004+2025, for which we give priority to the NAL detection in the legend. The upper panel reports the fraction of quasars displaying outflow detections in absorption as a function of Δv(C IV-Mg II).