  We present updated results for the nucleon axial charge and electromagnetic
(EM) form factors, which include a significant increase in statistics for all
ensembles (up to 4000 measurements), as well as the addition of ensembles with
pion masses down to $m_\pi\sim195$ MeV. We also present results for the average
quark momentum fraction. The new data allows us to perform a thorough study of
the systematic effects encountered in the lattice extraction. We concentrate on
systematic effects due to excited-state contaminations for each of the
quantities, which we check using several different time separations between the
operators at the source and sink through a comparison of plateau fits and the
summed operator insertion method (which provides a mechanism to suppress the
excited-state contamination). We confirm our earlier finding that a reliable
extraction of the axial charge must be based on a method which eliminates
excited-state contaminations. Similar conclusions apply to our EM form factor
calculations . The measurements are calculated using the CLS ensembles with
non-perturbatively O(a) improved Wilson fermions in $N_f=2$ QCD.
