  Using the (2+1)-dimensional viscous hydrodynamic code VISH2+1, we present
systematic studies of the dependence of pion and proton transverse momentum
spectra and their elliptic flow in 200 A GeV Au+Au collisions on the parameters
of the hydrodynamic model (thermalization time, initial entropy density
distribution, decoupling temperature, equation of state, and specific shear
viscosity eta/s). We identify a tension between the slope of the proton
spectra, which (within hydrodynamic simulations that assume a constant shear
viscosity to entropy density ratio) prefer larger eta/s values, and the slope
of the p_T-dependence of charged hadron elliptic flow, which prefers smaller
values of eta/s. Changing other model parameters does not appear to permit
dissolution of this tension
