  Recent hexadecapole (v4) and elliptic (v2) flow measurements are used to
constrain estimates for the degree of local equilibrium, mean free path
$\lambda$, and the viscosity to entropy density ratio (eta/s) of the plasma
produced in Au+Au collisions at RootS = 200 GeV. The eccentricity-scaled flow
coefficients v2/e2 and v4/e4 indicate that the plasma achieves a degree of
local equilibrium within 5 - 10% of the value expected for a fluid with eta/s
equal to the conjectured lower bound of 1/4pi. Estimates for $\lambda$ and
eta/s as a function of collision centrality and particle transverse momentum
pT, points to transverse expansion dynamics compatible with a strongly coupled
low viscosity plasma.
