Rate constants have been numerically computed for a cubic oscillator subject to a Gaussian friction kernel. The system is studied over a wide range of system-bath coupling, as measured by the static friction coefficient, and the obtained rate constants are compared with theoretical predictions as well as with previous simulations. The results are consistent with variational bounds in the spatial diffusion regime; values lower or equal to the theoretical estimates are obtained throughout. This should resolve the paradox that existed for very high friction, where values higher than the theoretical predictions has been reported and tentatively assigned to a possible nonergodicity of the model. The origin of the discrepancy between the present results and previous simulations, together with the range of validity of several theoretical approaches, are discussed.