I think you will find rigidity to be an issue in the dovetail ways more than the machine itself moving. I have a metal base that I build for mine and while it may not weigh 400+ lbs, it does add a lot to the machine itself. I hate standard bases that come with machines. They are usually lightweight and have very little in the way of functionality.
Honestly, right now I am chasing some rigidity issues with my 833T. Mine is solely in the dovetail ways though and predominantly in the Z axis. Finding that balance of gib adjustment is challenging. I have even considered even doing a linear guide conversion to the Z, but that would require some major rework and I certainly have not exhausted my options with the gibs yet.