Thanks everyone for your thoughts and tests. I had my friend send me the scene and I am rendering it and checking how it syncs with the back-plate in After Effects. I didn't touch the motion blur settings other that turning it on. So far, it looks okay but it does also appear to float a touch, seeming to pr-empt the camera motion on certain jerky frames. So finding the correct motion blur setting is some kind of art it seems, and Vray has quite a few MB settings.
I think the tests above show how crucial this can be, however I would actually render without MB and add it in post for the type of shot this is, the Re-vision plugin is doing a very nice match from what I can tell, I'll let this render go to the end and then render out a pass with no MB and apply the post motion blur, I have a feeling it will do a better job and be quicker.
It's a shame Vray doesn't interpret the correct blur settings based on the camera settings automatically. Post motion blur isn't always the way to go.