  We solve renormalization group equations that govern infrared divergences of
massless and massive form factors. By comparing to recent results for planar
massive three-loop and massless four-loop form factors in QCD, we give
predictions for the high-energy limit of massive form factors at the four- and
for the massless form factor at five-loop order. Furthermore, we discuss the
relation which connects infrared divergences regularized dimensionally and via
a small quark mass and extend results present in the literature to higher
order.
