  We explore potential strategies for testing General Relativity via the
coherent motions of galaxies. Our position at z=0 provides the reference point
for distance measures in cosmology. By contrast, the Cosmic Microwave
Background at z ~ 1100 acts as the point of reference for the growth of large
scale structure. As a result, we find there is a lack of synergy between growth
and distance measures. We show that when measuring the gravitational growth
index gamma using redshift-space distortions, typically 80% of the signal
corresponds to the local growth rate at the galaxy bin location, while the
remaining fraction is determined by its behaviour at higher redshifts.
  In order to clarify whether modified gravity may be responsible for the dark
energy phenomenon, the aim is to search for a modification to the growth of
structure. One might expect the magnitude of this deviation to be commensurate
with the apparent dark energy density Omega_Lambda(z). This provides an
incentive to study redshift-space distortions (RSD) at as low a redshift as is
practical. Specifically, we find the region around z = 0.5 offers the optimal
balance of available volume and signal strength.
