  Within a parton cascade we investigate the dependence of anisotropies in
momentum space, namely the elliptic flow $v_2=<cos(2\phi)>$ and the
$v_4=<cos(4\phi)>$, on both the finite shear viscosity $\eta$ and the
freeze-out (f.o.) dynamics at the RHIC energy of 200 AGeV. In particular it is
discussed the impact of the f.o. dynamics looking at two different procedures:
switching-off the collisions when the energy density goes below a fixed value
or reducing the cross section according to the increase in $\eta/s$ from a QGP
phase to a hadronic one. We address the relation between the scaling of
$v_2(p_T)$ with the eccentricity $\epsilon_x$ and with the integrated elliptic
flow. We show that the breaking of the $v_2(p_T)/\epsilon_x$ scaling is not
coming mainly from the finite $\eta/s$ but from the f.o. dynamics and that the
$v_2(p_T)$ is weakly dependent on the f.o. scheme. On the other hand the
$v_4(p_T)$ is found to be much more dependent on both the $\eta/s$ and the f.o.
dynamics and hence is indicated to put better constraints on the properties of
the QGP. A first semi-quantitative analysis show that both $v_2$ and $v_4$
(with the smooth f.o.) consistently indicate a plasma with $4\pi \eta/s \sim
1-2$.
