Of course a different slit width influences the spectral recording behaviour. Indeed to better compare the two spectra I recommend converting the X-axis scale to Å and dito cropping between 6520 – 6620Å. However the spectral information of both spectra is very similar, taking in account the different moment of observation.
Increasing the slit width increases the incident light intensity and amplitude, but in this case slightly decreasing the Resolving Power. The incident light intensity increases proportional to the square of the slit width, so a compromise must be made to end up with a nice PSF,a good spectral baseline and SNR. In case of the newest CMOS camera’s impressive reduction of exposure times can be reached by optimal gain settings, cooling to -20 C° and appropriate dew/condense control.