  We present an investigation of charge-compensated antiferromagnetic
(Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_{3}$O$_{y}$ single crystals
using Raman scattering as well as muon spin rotation. In this system the
parameter $x$ controls the Cu-O-Cu superexchange interaction via bond distances
and buckling angles. The oxygen content $y$ controls the charge doping. In the
absence of doping the two-magnon peak position is directly proportional to the
superexchange strength $J$. We find that both $x$ and $y$ affect the peak
position considerably. The N\'{e}el temperature determined from muon spin
rotation on the same samples independently confirms the strong dependence of
the magnetic interaction on $x$ and $y$. We find a considerable increase in the
maximum superconducting transition temperature $T_{c}^{max}$ with $J$. This is
strong evidence of the importance of orbital overlap to superconductivity in
this family of cuprates.
