As far as I know RSMB is, by far, the best thing you can get in terms of post motion blur.
If you are not using DOF or Motion Blur straight in Cinema there is no much need to use the physical renderer anyway. In R14 the image sampling process of the standard and physical renderer has been unified so it is more or less the same now. The motion vector pass should work fine with Cinema if used correctly. This has to do the fact that C4D spits files out in linear color space by default. To make it work you need to preserve the RGB values of special passes like the motion vector (or the z-depth pass) in the post process. If using After Effects, this can be selected in the color management tab of any imported footage. I found a tut that visually illustrates it: https://vimeo.com/33243611
Still, nothing is likely to beat the quality of the physically correct motion blur.
Hope I made some sense. Good luck!