  This paper presents new optical and near-UV spectra of 11 extremely powerful
jetted quasars, with radio to optical flux density ratio $>$ 10$^3$, that
concomitantly cover the low-ionization emission of \mgii\ and \hb\ as well as
the \feii\ blends in the redshift range $0.35 \lesssim z \lesssim 1$. We aim to
quantify broad emission line differences between radio-loud (RL) and
radio-quiet (RQ) quasars by using the 4D eigenvector 1 parameter space and its
Main Sequence (MS) and to check the effect of powerful radio ejection on the
low ionization broad emission lines. The \hb\ and \mgii\ emission lines were
measured by using non-linear multicomponent fittings as well as by analysing
their full profile. We found that broad emission lines show large redward
asymmetry both in \hb\ and \mgii. The location of our RL sources in a UV plane
looks similar to the optical one, with weak \feiiuv\ emission and broad \mgii.
We supplement the 11 sources with large samples from previous work to gain some
general inferences. We found that, compared to RQ, our extreme RL quasars show
larger median \hb\ full width at half maximum (FWHM), weaker \feii\ emission,
larger \mbh, lower \lledd, and a restricted bf space occupation in the optical
and UV MS planes. The differences are more elusive when the comparison is
carried out by restricting the RQ population to the region of the MS occupied
by RL sources, albeit an unbiased comparison matching \mbh\ and \lledd\
suggests that the most powerful RL quasars show the highest redward asymmetries
in \hb.
